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JIG AND FIXTURE
DESIGN

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JIG AND FIXTURE DESIGN

ior\ ,

JIG AND FIXTURE
DESIGN

A TREATISE COVERING THE PRINCIPLES OF
JIG AND FIXTURE DESIGN, THE IMPORTANT
CONSTRUCTIONAL DETAILS, AND MANY DIF-
FERENT TYPES OF WORK-HOLDING DEVICES
USED IN INTERCHANGEABLE MANUFACTURE

EDITED BY

FRANKLIN Df JONES

ASSOCIATE EDITOR OF MACHINERY

AUTHOR OF "TURNING AND BORING," "PLANING AND MILLING,

" MECHANISMS AND MECHANICAL MOVEMENTS,"

"THREAD-CUTTING METHODS," ETC.

FIRST EDITION

NEW YORK
THE INDUSTRIAL PRESS

LONDON: THE MACHINERY PUBLISHING CO., LTD.
I Q2O

THE INDUSTRIAL PRESS
NEW YORK

COMPOSITION AND ELECTROTYPING BY THE PLIMPTON PRESS, NORWOOD, MASS., U. S. A.

PREFACE

The development of machine tools has been accompanied
by a corresponding development of auxiliary equipment for in-
creasing the quantity and improving the quality of the products
of these machines. Whenever duplicate parts require some
operation such as drilling, planing, or milling, the selection
of a suitable type of machine is often followed by the design
of whatever special tools or attachments are needed to adapt
the machine to the operation required. The tool-guiding and
work-holding jigs and fixtures which are now used in prac-
tically all machine shops represent the most important class
of special equipment, and this book deals exclusively with
their design and construction.

As most jigs are used for drilling operations, a book was
previously published entitled "Drilling Practice and Jig De-
sign," covering different types of drilling machines and their
use, the design of drill jigs, and, to some extent, the design of
fixtures such, for example, as are used on milling machines.
While the subjects of drilling and jig design are closely allied,
it is no longer possible to cover them both in a single volume,
owing to the extensive changes in drilling practice and the
increasing use of jigs and fixtures of various types on different
classes of machine tools. Therefore, the book referred to has
been replaced by two volumes, of which this is one. The other
book, "Modern Drilling Practice," is already well known to
many designers, shop foremen, and machinists interested in
the latest types of drilling machines and their use.

This new book, "Jig and Fixture Design," contains that
part of the volume on "Drilling Practice and Jig Design" which
dealt with jigs and fixtures. This material was used because it
is a treatise on the principles of jig and fixture design which
contains information that is indispensable in a book of this

VI PREFACE

kind. These original chapters which explain the general pro-
cedure in designing jigs and fixtures and how work should be
located, clamped, etc.,' have been supplemented by a large
amount of new matter, thus making the present book unusually
complete. A great variety of jig and fixture designs have been
described and illustrated in order to show just how the principles
and important details referred to in the forepart of the book are
applied under many different conditions and to jigs and fixtures
used on various types of machine tools.

Most of the designs illustrated in this book have been sent
to MACHINERY from men in the machine-building field, be-
cause the designs were considered unusual and worth placing
on record. While it would not be possible to give credit to
each individual contributor, we are indebted to all who have
assisted indirectly in preparing this treatise, and especially to
Einar Morin and Albert A. Dowd, recognized tool experts and
production engineers, who have supplied valuable material for
several of the chapters on jig design.

THE EDITOR.

New York, October, 1920.

CONTENTS
CHAPTER I

PAGES

PRINCIPLES OF JIG DESIGN

Objects of Jigs and Fixtures — Difference between Jigs
and Fixtures — Fundamental Principles of Jig Design —
Locating Points — Clamping Devices — Weight of Jigs —
Jigs provided with Feet — Materials for Jigs — General
Remarks on Jig Design — Summary of Principles of Jig
Design — Types of Jigs — Open Jigs — Box Jigs — De-
tails of Jig Design 1-20

CHAPTER II
DESIGN OF OPEN DRILL JIGS

Jig Drawings — Designing Open Jigs — Improving the
Simple Form of Jig by Adding Locating Screws — Pro-
viding Clamps and Feet for the Jig — Examples of Open
Drill Jigs 21-44

CHAPTER III
DESIGN OF CLOSED OR BOX JIG

General Procedure in the Design of Closed or Box Jigs -
Jigs for Rapid Production — Special Features of Box Jigs
— Examples of Closed or Box Jigs 45-6?

CHAPTER IV
JIG BUSHINGS

Removable Bushings — Material for Jig Bushings -
Dimensions of Stationary Jig Bushings — Miscellaneous
Types of Jig Bushings — Means for Preventing Loose
Bushings from Turning — Dimensions of Removable Bush-
ings — Screw Bushings — Special Designs of Guide Bush-
ings — Methods of making Jig Bushings — Hardening Jig
Bushings — Grinding and Lapping. .... 68-91

vii

Viii CONTENTS

CHAPTER V

LOCATING POINTS AND ADJUST-
ABLE STOPS PAGES

Pins and Stops used as Locating Means — Locating by
Means of V-blocks — Cup and Cone Locating Points —
Screw Bushings and Sliding Bushings used as Locating
Means — Adjustable Locating Points — Special Types of
Adjustable Stops — Locating from Finished Holes — Lo-
cating by Keyways in the Work — Common Defects in
Jig Design 92-109

CHAPTER VI
JIG CLAMPING DEVICES

Types of Clamps — Hook-bolts — Screw-tightening De-
vices — Swinging Leaves — Wedge or Taper Gibs — Ec-
centric Clamping Arrangements — Applications to Jig
Design 110-150

CHAPTER VII
EXAMPLES OF DRILL JIG DESIGN

Different Types of Indexing Jigs — Jig for Deep-hole
Drilling — Jig of Simple Design for drilling Straight and
Angular Holes — Drill Jig equipped with Milling Attach-
ment—Jig for Cross-drilling Pistons and Facing Wrist-
pin Bosses — Universal Jigs — Machine Vises with Drill
Jig Attachments — Miscellaneous Designs 151-194

CHAPTER VIII
BORING JIGS

Boring Jig of Simple Design — Adjustable Boring Jigs -
Boring Jig supported on Work — Jigs designed for Sup-
porting Bar on One Side of Hole Only — Jigs for Multiple
Boring — Combination Drill and Boring Jig 195-210

CONTENTS ix

CHAPTER IX

MILLING AND PLANING FIXTURES PAGES

Fixture for milling to a Given Length — Duplex Fixture
-Adjustable Fixture for Angular Work — Fixture ar-
ranged for Lateral and Angular Adjustment — Indexing
Milling Fixtures — Various Designs of Radial Milling
Fixtures — Examples of Planer Fixture Design 211-241

CHAPTER X

ADJUSTABLE FIXTURES FOR TURRET LATHES
AND VERTICAL BORING MILLS

Important Points in the Design — Adjustable Fixture
for Holding Castings of Different Diameters — Adjustable
Fixture for Special Bevel Gear Blanks — Provision for
maintaining Accuracy in Adjustable Fixture — Various
Designs of Adjustable Fixtures for Vertical Boring Mills. . . 242-256

CHAPTER XI

THE FLOATING PRINCIPLE AS APPLIED
TO FIXTURE WORK

Important Points in the Application of Floating Principle
— Piston Drill Jig with Floating Clamps — Drill Jig for
Rough Collar — Drill Jig with Floating Bushings and
Locating Vees — Milling Fixture with Floating Clamps
and Locator — Various other Designs of Locating Devices
illustrating the Application of the Floating Principle 257-275

CHAPTER XII

APPLICATION OF THE THREE-POINT PRINCI-
PLE IN FIXTURES

Three-point Locating and Clamping Devices — Three-
point Support for Flywheel Fixture — Three-point Fixture
for Pot Casting — Two Methods of Obtaining a Three-point
Support on a Hub Casting — Fixture having Three Clamp-
ing Jaws and Three Locating Pads — Double Three-point
Locating Device 276-287

X CONTENTS

, CHAPTER XIII

SPECIAL JIG AND FIXTURE MECHANISMS PAGES

Equalizing the Pressure of Clamping Devices — Clamps
that draw the Work down Firmly on the Locating
Means — Multiple-clamping Devices — Clamping Devices
for Fixtures that do not interfere with the Tools used —
Three-point Clamping Devices 288-305

CHAPTER XIV

PROVIDING FOR UPKEEP IN DESIGNING JIGS
AND FIXTURES

Points Pertaining to Upkeep — Drill Jig for a Receiver
Forging — Drilling and Reaming Jig — Indexing Fixture
for a Clutch Gear — Fixture with Inserted Jaws — Bevel
Gear Fixture with Adjustable Features — Fixture for a
Hub Casting 306-315

JIG AND FIXTURE DESIGN

CHAPTER I
PRINCIPLES OF JIG DESIGN

Jigs and fixtures may be defined as devices used in the manu-
facture of duplicate parts of machines and intended to make
possible interchangeable work at a reduced cost, as compared
with the cost of producing each machine detail individually.
Jigs and fixtures serve the purpose of holding and properly locat-
ing a piece of work while machined, and are provided with neces-
sary, appliances for guiding, supporting, setting, and gaging the
tools in such a manner that all the work produced in the same
jig or fixture will be alike in all respects, even with the employ-
ment of unskilled labor. When using the expression "alike,"
it implies, of course, simply that the pieces will be near enough
alike for the purposes for which the work being machined is
intended. Thus, for certain classes of work, wider limits of
variation will be permissible without affecting the proper use
of the piece machined, while in other cases the limits of varia-
tion will be so small as to make the expression "perfectly alike"
literally true.

Objects of Jigs and Fixtures. — The main object of using jigs
and fixtures is the reduction of the cost of machines or machine
details made in great numbers. This reduction of cost is ob-
tained in consequence of the increased rapidity with which the
machines may be built and the employment of cheaper labor,
which is possible when using tools for interchangeable manu-
facturing. Another object, not less important, is the accuracy
with which the work can be produced, making it possible to
assemble the pieces produced in jigs without any great amount of
fitting in the assembling department, thus also effecting a great
saving in this respect. The use of jigs and fixtures practically
does away with the fitting, as this expression was understood in
the old-time shop; it eliminates cut-and-try methods, and does

2 JIG DESIGN

away with so-called "patch- work" in the production of machin-
ery. It makes it possible to have all the machines built in the
shop according to the drawings, a thing which is rather difficult
to do if each individual machine in a large lot is built without
reference to the other machines in the same lot.

The interchangeability obtained by the use of jigs and fixtures
makes it also an easy matter to quickly replace broken or worn-
out parts without great additional cost and trouble. When
machines are built on the individual plan, it is necessary to fit
the part replacing the broken or worn-out piece, in place, involv-
ing considerable extra expense, not to mention the delay and the
difficulties occasioned thereby.

As mentioned, jigs and fixtures permit the employment of
practically unskilled labor. There are many operations in the
building of a machine, which, if each machine were built indi-
vidually, without the use of special tools, would require the work
of expert machinists and toolmakers. Special tools, in the form
of jigs and fixtures, permit equally good, or, in some cases, even
better results to be obtained by a much cheaper class of labor,
provided the jigs and fixtures are properly designed and cor-
rectly made. Another possibility for saving, particularly in the
case of drill and boring jigs provided with guide bushings in the
same plane, is met with in the fact that such jigs are adapted to
be used in multiple-spindle drills, thereby still more increasing
the rapidity with which the work may be produced. In shops
where a great many duplicate parts are made, containing a
number of drilled holes, multiple-spindle drills of complicated
design, which may be rather expensive as regards first cost, are
really cheaper, by far, than ordinary simple drill presses.

Another advantage which has been gained by the use of jigs
and fixtures, and which should not be lost sight of in the enu-
meration of the points in favor of building machinery by the use
of special tools, is that the details of a machine that has been
provided with a complete equipment of accurate and durable
jigs and fixtures can all be finished simultaneously in different
departments of a large factory, without inconvenience, thus mak-
ing it possible to assemble the machine at once after receiving

JIG DESIGN 3

the parts from the different departments; and there is no need
of waiting for the completion of one part into which another is
required to fit, before making this latter part. This gain in
time means a great deal in manufacturing, and was entirely
impossible under the old-time system of machine building, when
each part had to be made in the order in which it went to
the finished machine, and each consecutive part had to be lined
up with each one of the previously made and assembled details.
Brackets, bearings, etc., had to be drilled in place, often with
ratchet drills, which is a slow and always inconvenient operation.

Difference between Jigs and Fixtures. — To exactly define
the word "jig, " as considered apart from the word "fixture,"
is difficult, as the difference between a jig and a fixture is often-
times not very easy to decide. The word jig is frequently, al-
though incorrectly, applied to any kind of a work-holding appli-
ance used in the building of machinery, the same as, in some
shops, the word fixture is applied to all kinds of special tools.
As a general rule, however, a jig is a special tool, which, while it
holds the work, or is held onto the work, also contains guides
for the respective tools to be used; whereas a fixture is only
holding the work while the cutting tools are performing the oper-
ation on the piece, without containing any special arrangements
for guiding these tools. The fixture, therefore, must, itself, be
securely held or fixed to the machine on which the operation is
performed; hence the name. A fixture, however, may sometimes
be provided with a number of gages and stops, although it does
not contain any special devices for the guiding of the tools.

The definition given, in a general way, would therefore clas-
sify jigs as special tools used particularly in drilling and boring
operations, while fixtures, in particular, would be those special
tools used on milling machines, and, in some cases, on planers,
shapers, and slotting machines. Special tools used on the lathe
may be either of the nature of jigs or fixtures, and sometimes the
special tool is actually a combination of both, in which case the
term drilling fixture, boring fixture, etc., is suitable.

Fundamental Principles of Jig Design. — Before entering
upon a discussion of the minor details of the design of jigs and

4 JIG DESIGN

fixtures, the fundamental principles of jig and fixture design
will be briefly outlined. Whenever a jig is made for a compo-
nent part of a machine, it is almost always required that a corre-
sponding jig be made up for the place on the machine, or other
part, where the first-mentioned detail is to be attached. It is,
of course, absolutely necessary that these two jigs be perfectly
alike as to the location of guides and gage points. In order 'to
have the holes and guides in the two jigs in alignment, it is advis-
able, and almost always cheaper and quicker, to transfer the
holes or the gage points from the first jig made to the other. In
many instances, it is possible to use the same jig for both parts.
Cases where the one or the other of these principles is applicable
will be shown in the following chapters in the detailed descrip-
tions of drill and boring jigs.

There are some cases where it is not advisable to make two
jigs, one for each of the two parts which are to fit together. It
may be impossible to properly locate the jig on one of the parts
to be drilled, or, if the jig were made, it may be so complicated
that it would not be economical. Under such conditions the
component part itself may be used as a jig, and the respective
holes in this part used as guides for the tools when machining
the machine details into which it fits. Guide bushings for the
drills and boring bars may then be placed in the holes in the
component part itself. In many cases, drilling and boring opera-
tions are also done, to great advantage, by using the brackets
and bearings already assembled and fastened to the machine
body as guides.

One of the most important questions to be decided before mak-
ing a jig is the amount of money which can be expended on a
special tool for the operation required. In many cases, it is
possible to get a highly efficient tool by making it more compli-
cated and more expensive, whereas a less efficient tool may be
produced at very small expense. To decide which of these two
types of jigs and fixtures should be designed in each individual
case depends entirely upon the circumstances. There should be
a careful comparison of the present cost of carrying out a certain
operation, the expected cost of carrying out the same operation

JIG DESIGN 5

with an efficient tool, and the cost of building that tool itself.
Unless this is done, it is likely that the shop is burdened with a
great number of special tools and fixtures which, while they
may be very useful for the production of the parts for which they
are intended, actually involve a loss. It is readily seen how
uneconomical it would be to make an expensive jig and fixture
for a machine or a part of a machine that would only have to
be duplicated a few times. In some cases, of course, there may
be a gain in using special devices in order to get extremely good
and accurate results.

Locating Points. — The most important requirements in the
design of jigs are that good facilities be provided for locating the
work, and that the piece to be machined may be easily inserted
and quickly taken out of the jig, so that no time is wasted in
placing the work in position on the machine performing the work.
In some cases, a longer time is required for locating and clamp-
ing the piece to be worked upon than is required for the actual
machine operation itself. In all such cases the machine per-
forming the work is actually idle the greater part of the time, and,
added to the loss of the operator's time, is the increased expense
for machine cost incurred by such a condition. For this reason,
the locating and clamping of the work in place quickly and
accurately should be carefully studied by the designer before
any attempt is made to design the tool. In choosing the locat-
ing surface or points of the piece or part, consideration must be
given to the facilities for locating the corresponding part of the
machine in a similar manner. It is highly important that this
be done, as otherwise, although the jigs may be alike, as far as
their guiding appliances are concerned, there may be no facility
for locating the corresponding part in the same manner as the
one already drilled, and while the holes drilled may coincide,
other surfaces, also required to coincide, may be considerably
out of line. One of the main principles of location, therefore,
is that two component parts of the machine should be located
from corresponding points and surfaces.

If possible, special arrangements should be made in the design
of the jig so that it is impossible to insert the piece in any but

6 JIG DESIGN

the correct way. Mistakes are often made on this account
in shops where a great deal of cheap help is used, pieces being
placed in jigs upside down, or in some way other than the cor-
rect one, and work that has been previously machined at the
expenditure of a great deal of time is entirely spoiled. There-
fore, whenever possible, a jig should be made " fool-proof ."

When the work to be machined varies in shape and size, as,
for instance, in the case of rough castings, it is necessary to have
at least some of the locating points adjustable and placed so
that they can be easily reached for adjustment, but, at the same
time, so fastened that they are, to a certain extent, positive. In
the following chapters different kinds of adjustable locating
points will be described in detail.

Clamping Devices. — The strapping or clamping arrangements
should be as simple as possible, without sacrificing effectiveness,
and the strength of the clamps should be such as to not only hold
the piece firmly in place, but also to take the strain of the cutting
tools without springing or " giving." When designing the jig,
the direction in which the strain of the tool or cutters acts upon
the work should always be considered, and the clamps so placed
that they will have the highest degree of strength to resist the
pressure of the cut.

The main principles in the application of clamps to a jig or
fixture are tha£ they should be convenient for the operator,
quickly operated, and, when detached from the work, still con-
nected with the jig or fixture itself, so as to prevent the oper-
ator from losing them. Many a time, looking for lost straps,
clamps, screws, etc., causes more delay in shops than the extra
cost incurred in designing a jig or fixture somewhat more com-
plicated, in order to make the binding arrangement an integral
part of the fixture itself. Great complication in the clamping
arrangements, however, is not advisable. Usually clamping
arrangements of this kind work well when the fixture is new, but,
as the various parts become worn, complicated arrangements
are more likely to get out of order, and the extra cost incurred in
repairing often outweighs the temporary gain in quickness of
operation.

JIG DESIGN 7

The judgment of the designer is, in every case, the most im-
portant point in the design of jigs and fixtures. Definite rules
for all cases cannot be given. General principles can be studied,
but the efficiency of the individual tool will depend entirely upon
the judgment of the tool designer in applying the general prin-
ciples of tool design to the case in hand.

When designing the jig or fixture, the locating and bearing
points for the work and the location of the clamps must also be
so selected that there is as little liability as possible of springing
the piece or jig, or both, out of shape, when applying the clamps.
The springing of either the one or the other part will cause in-
correct results, as the work surfaces will be out of alignment with
the holes drilled or the faces milled. The clamps or straps
should therefore, as far as possible, be so placed that they are
exactly opposite some bearing point or surface on the work.

Weight of Jigs. — The designer must use his judgment in re-
gard to the amount of metal put into the jig or fixture. It is
desirable to make these tools as light as possible, in order that
they may be easily handled, be of smaller size, and cost less in
regard to the amount of material used for their making, but, at
the same time, it is poor economy to sacrifice any of the rigidity
and stiffness of the tool, as this is one of the main considerations
in obtaining efficient results. On large-sized jigs and fixtures,
it is possible to core out the metal in a number of places, without
decreasing, in the least, the strength of the jig itself. The
corners of jigs and fixtures should always be well rounded, and
all burrs and sharp edges filed off, so as to make them convenient
and pleasant for handling. Smaller jigs should also be made
with handles in proper places, so that they may be held in posi-
tion while working, as in the case of drilling jigs, and also for
convenience in moving the jig about.

Jigs Provided with Feet. — Ordinary drill jigs should always
be provided with feet or legs on all sides which are opposite the
holes for the bushings, so that the jig can be placed level on the
table of the machine. These feet also greatly facilitate the
making of the jig, making it easier to lay out and plane the differ-
ent finished surfaces. On the sides of the jig where no feet are

8 JIG DESIGN

required, if the body is made from a casting, it is of advantage
to have small projecting lugs for bearing surfaces when laying
out and planing. While jigs are most commonly provided with
four feet on each side, in some cases it is sufficient to provide the
tool with only three feet, but care should be taken in either case
that all bushings and places where pressure will be applied to the
tool are placed inside of the geometrical figure obtained by con-
necting, by lines, the points of location for the feet.

While it may seem that three feet are preferable to use, because
the jig will then always obtain a bearing on all the three feet,
which it would not with four feet, if the table of the machine
were not absolutely plane, it is not quite safe to use the smaller
number of supports, because a chip or some other object is liable
to come under one foot and throw the jig and the piece out of
line, without this being noticed by the operator. If the same
thing happens to a jig with four feet, it will rock and invariably
cause the operator to notice the defect. If the table is out of
true, this defect, too, will be noticed for the same reason.

Jig feet are generally cast solid with the jig frame. When the
jig frame is made from machine steel, and sometimes in the case
of cast-iron jigs, detachable feet are used.

Materials for Jigs. — Opinions differ as to the relative merits
of cast iron and steel as materials from which to construct the
jig and fixture bodies. The decision on this point should depend
to a great extent upon the usage to which the fixture is to be put
and the character of the work which it is to handle. For small
and medium sized work, such as typewriter, sewing machine,
gun, adding machine, cash register, phonograph, and similar
parts, the steel jig offers decided advantages, but for larger work,
such as that encountered in automobile, engine, and machine tool
fixtures, the cast-iron jig is undoubtedly the cheaper and more
advisable to use. The steel jig should be left soft in order that
at any future time additional holes may be added, or the existing
bushings changed as required. With a cast-iron jig this adding
of bushings is a difficult matter, as the frame is usually bossed
and "spot finished" at the point where the bushings are located,
and it is very difficult to build up on the jig frame in order to

JIG DESIGN 9

locate or change the bushings. When designing the jig, these
points should be remembered and provision made for them,
where possible.

General Remarks on Jig Design. — One mistake, quite fre-
quently made, is that of giving too little clearance between the
piece to be machined and the walls or sides of the jig used for it.
Plenty of clearance should always be allowed, particularly when
rough castings are being drilled or machined in the jigs; besides,
those surfaces in the jig which do not actually bear upon the
work do not always come exactly to the dimensions indicated on
the drawing, particularly in a cast-iron jig, and allowance ought
to be made for such differences.

In regard to the locating points, it ought to be remarked that,
in all instances, these should be visible to the operator when
placing the work in position, so that he may be enabled to see
that the work really is in its right place. At times the construc-
tion of the piece to be worked upon may prevent a full view of
the locating points. In such a case a cored or drilled hole in the
jig, near the locating seat, will enable a view of same, so that the
operator may either see that the work rests upon the locating
point, or so that he can place a feeler or thickness gage between
the work and the locating surface, to make sure that he has the
work in its correct position. Another point that should not be
overlooked is that jigs and fixtures should be designed with a view
of making them easily cleaned from the chips, and provision
should also be made so that the chips, as far as possible, may fall
out of the jig and not accumulate on or about the locating points,
where they are liable to throw the work out of its correct position
and consequently spoil the piece.

The principles so far referred to have all been in relation to
the holding of the work in the jig, and the general design of the
jig for producing accurate work. Provisions, however, should
also be made for clamping the jig or fixture to the table of the
machine, in cases where it is necessary to have the tool fixed
while in operation. Small drilling jigs are not clamped to the
table, but boring jigs and milling and planing fixtures invariably
must be firmly secured to the machine on which they are used.

10 JIG DESIGN

Plain lugs, projecting out in the same plane as the bottom of
the jig, or lugs with a slot in them to fit the body of T-bolts, are
the common means for clamping fixtures to the table. For
boring jigs, it is unnecessary to provide more than three such
clamping points, as a greater number is likely to cause some
springing action in the fixture. A slight springing effect is almost
unavoidable, no matter how strong and heavy the jig is, but, by
properly applying the clamps, it is possible to confine this spring-
ing within commercial limits.

Jigs should always be tested before they are used, so as to
make sure that the guiding provisions are placed in the right
relation to the locating points and in proper relation to each
other.

Summary of Principles of Jig Design. — Summarizing the
principles referred to, the following rules may be given as the main
points to be considered in the designing of jigs and fixtures:

1. Before planning the design of a tool, compare the cost of
production of the work with present tools with the expected cost
of production, using the tool to be made, and see that the cost of
building is not in excess of expected gain.

2. Before laying out the jig or fixture, decide upon the locat-
ing points and outline a clamping arrangement.

3. Make all clamping and binding devices as quick-acting
as possible.

4. In selecting locating points, see that two component parts
of a machine can be located from corresponding points and sur-
faces.

5. Make the jig " fool-proof "; that is, arrange it so that the
work cannot be inserted except in the correct way.

6. For rough castings, make some of the locating points
adjustable.

7. Locate clamps so that they will be in the best position to
resist the pressure of the cutting tool when at work.

8. Make, if possible, all clamps integral parts of the jig or
fixture.

9. Avoid complicated clamping arrangements, which are
liable to wear or get out of order.

JIG DESIGN II

10. Place all clamps as nearly as possible opposite some
bearing point of the work, to avoid springing.

11. Core out all unnecessary metal, making the tools as light
as possible, consistent with rigidity and stiffness.

12. Round all corners.

13. Provide handles wherever these will make the handling
of the jig more convenient.

14. Provide feet, preferably four, opposite all surfaces con-
taining guide bushings in drilling and boring jigs.

15. Place all bushings inside of the geometrical figure formed
by connecting the points of location of the feet.

1 6. Provide abundant clearance, particularly for rough
castings.

17. Make, if possible, all locating points visible to the operator
when placing the work in position.

18. Provide holes or escapes for the chips.

19. Provide clamping lugs, located so as to prevent spring-
ing of the fixture, on all tools which must be held to the table
of the machine while in use, and tongues for the slots in the
tables in all milling and planing fixtures.

20. Before using in the shop, for commercial purposes, test
all jigs as soon as made.

Types of Jigs. — The two principal classes of jigs are drill
jigs and boring jigs. Fixtures may be grouped as milling,
planing, and splining fixtures, although there are a number of
special fixtures which could not be classified under any special
head.

Drill jigs are intended exclusively for drilling, reaming, tap-
ping, and facing. Whenever these four operations are required
on a piece of work, it is, as a rule, possible to provide the neces-
sary arrangements for performing all these operations in one
and the same jig. Sometimes separate jigs are made for each
one of these operations, but it is doubtless more convenient
and cheaper to have one jig do for all, as the design of the jig
will not be much more complicated. Although it may be pos-
sible to make a distinction between a number of different types
of drill jigs, it is almost impossible to define and to get proper

12 JIG DESIGN

names for the various classes, owing to the great variety of
shapes of the work to be drilled. There are, however, two general
types that are most commonly used, the difference between
them being very marked. These types may be classified as
open jigs and closed jigs, or box jigs. Sometimes the open jigs
are called clamping jigs. The open jigs usually have all the drill
bushings in the same plane, parallel with one another, and are
not provided with loose or removable walls or leaves, thereby
making it possible to insert the piece to be drilled without any
manipulation of the parts of the jig. These jigs are often of
such a construction that they are applied to the work to be
drilled, the jig being placed on the work, rather than the work
being placed in the jig. The jig may be held to the work by
straps, bolts, or clamps, but in many cases the jig fits into or
over some finished part of the work and in this way the jig is
located and held in position.

The closed drill jigs, or box jigs, frequently resemble some
form of a box and are intended for pieces where the holes are
to be drilled at various angles to one another. As a rule, the
piece to be drilled can be inserted in the jig only after one or
more leaves or covers have been swung out of the way. Some-
times it is necessary to remove a loose wall, which is held by
bolts and dowel pins, in order to locate the piece in the jig.
The work in the closed drill jig may be held in place by set-
screws, screw bushings, straps, or hook-bolts.

The combination drilling and boring jig is another type of
closed jig designed to serve both for drilling and boring opera-
tions. Before designing a combination drill and boring jig,
the relation between, and number of, the drilled and bored
holes must be taken into consideration, and also the size of the
piece to be machined. In case there is a great number of holes,
it may be of advantage to have two or even more jigs for the
same piece, because it makes it easier to design and make the
jig, and very likely will give a better result. The holes drilled
or bored in the first jig may be used as a means for locating the
piece in the jigs used later on. Combination drill and boring
jigs are not very well adapted for pieces of large size.

JIG DESIGN

Open Jigs. — Open jigs of the simpler forms are simply
plates provided with bushed holes which are located to cor-
respond with the required locations for the drilled holes. While
holes are sometimes drilled by first laying out the holes directly
upon the work, it is quite evident that this method of drilling
would not be efficient if a large number of duplicate parts had
to be drilled accurately, as there is likely to be more or less
variation in the location of the holes, and considerable loss of
time. In the first place, a certain amount of time is required
for laying out these holes preparatory to drilling. The operator,

Fig. 1. Jig for Cylinder Flange and Head, and its Application

when starting the drill, must also be careful to make it cut
concentric with the scribed circle, which requires extra time,
and there will necessarily be more or less variation. To over-
come these objections, jigs are almost universally used for hold-
ing the work and guiding the drill, when drilling duplicate parts,
especially when quite a large number of duplicate pieces must
be drilled.

The ring-shaped jig shown at A in Fig. i is used for drilling
the stud bolt holes in a cylinder flange and also for drilling the
cylinder head, which is bolted to the cylinder. The position of

JIG DESIGN

the jig when the cylinder flange is being drilled is shown at
B. An annular projection on the jig fits closely in the cylinder
counterbore, as the illustration shows, to locate the jig concentric
with the bore. As the holes in the cylinder are to be tapped or
threaded for studs, a "tap drill," which is smaller in diameter
than the bolt body, is used and the drill is guided by a remov-
able bushing b of the proper size. Jigs of this type are often
held in position by inserting an accurately fitting plug through
the jig and into the first hole drilled, which prevents the jig
from turning with relation to the cylinder, when drilling the
other holes. When the jig is used for drilling the head, the

opposite side is placed
next to the work, as
shown at C. This side
has a circular recess or
counterbore, which fits
the projection on the
head to properly locate
the jig. As the holes in
the head must be slightly
larger in diameter than
the studs, another sized
drill and a guide bushing
of corresponding size are
used. The cylinder is, of
course, bored and the
head turned before the drilling is done.

Jigs of the open class, as well as those of other types, are
made in a great variety of shapes, and, when in use, they are
either applied to the work or the latter is placed in the jig.
When the work is quite large, the jig is frequently placed on it,
whereas small parts are more often held in the jig, which is so
designed that the work can be clamped in the proper position.
The form of any jig depends, to a great extent, on the shape of
the work for which it is intended and also on the location of
the holes to be drilled. As the number of differently shaped
pieces which go to make up even a single machine is often very

Fig. 2. Drill Jig of the Box Type

JIG DESIGN 15

great, and as most parts require more or less drilling, jigs are
made in an almost endless variety of sizes and forms. When all
the holes to be drilled in a certain part are parallel, and es-
pecially if they are all in the same plane, a very simple form of
jig can ordinarily be used.

Box Jigs. — A great many machine parts must be drilled on
different sides and frequently castings or forgings are very
irregular in shape, so that a jig which is made somewhat in

J L

Fig. 3. Box Jig for Drilling Ball shown enlarged at A

the form of a box, and encloses the work, is very essential, as
it enables the guide bushings to be placed on all sides and also
makes it comparatively easy to locate and securely clamp the
part in the proper position for drilling. This type of jig, which,
because of its form, is known as a closed or "box jig," is used
very extensively.

A box jig of simple design is shown in Fig. 2. This particu-
lar jig is used for drilling four small holes in a part (not shown)
which is located with reference to the guide bushings B by a
central pin A attached to the jig body. This pin enters a hole
in the work, which is finished in another machine in connection

JIG DESIGN

with a previous operation. After the work is inserted in the
jig, it is clamped by closing the cover C, which is hinged at one
end and has a cam-shaped clamping latch D at the other, that
engages a pin E in the jig body. The four holes are drilled by
passing the drill through the guide bushings B in the cover.

Another jig of the same kind, but designed for drilling a
hole having two diameters through the center of a steel ball,

Fig. 4. Box Jigs for Drilling Parts shown by Heavy Dot-and-dash Lines

is shown in Fig. 3. The work, which is shown enlarged at A,
is inserted while the cover is thrown back as indicated by the
dotted lines. The cover is then closed and tightened by the
cam-latch Z), and the large part of the hole is drilled with
the jig in the position shown. The jig is then turned over and
a smaller drill of the correct size is fed through guide bushing
B on the opposite side. The depth of the large hole could be
gaged for each ball drilled, by feeding the drill spindle down to
a certain position as shown by graduation or other marks, but

JIG DESIGN

if the spindle has an adjustable stop, this should be used. The
work is located in line with the two guide bushings by spherical
seats formed in the jig body and in the upper bushing, as shown.
As the work can be inserted and removed quickly, a large num-
ber of balls, which, practically speaking, are duplicates, can
be drilled in a comparatively short time by using a jig of this
type.

A box jig that differs somewhat in construction from the
design just referred to is illustrated at A in Fig. 4, which shows

Fig. 5. Jig shown at A, Fig. 4, in Two Different Drilling Positions

a side and top view. The work, in this case, is a small casting
the form of which is indicated by the heavy dot-and-dash lines.
This casting is drilled at a, b, and c, and the two larger holes a
and b are finished by reaming. The hinged cover of this jig
is opened for inserting the work by unscrewing the T-shaped
clamping screw s one-quarter of a turn, which brings the head
in line with a slot in the cover. The casting is clamped by tighten-
ing this screw, which forces an adjustable screw bushing g down
against the work. By having this bushing adjustable, it can
be set to give the right pressure, and, if the height of the cast-

1 8 JIG DESIGN

ings should vary, the position of the clamping bushing could
easily be changed.

The work is properly located by the inner ends of the three
guide bushings ai, bi, and ci, and also by the locating screws I
against which the casting is held by knurled thumb-screws m
and n. When the holes a and b are being drilled, the jig is
placed with the cover side down, as shown at A in Fig. 5, and
the drill is guided by removable bushings, one of which is shown
at r. When the drilling is completed, the drill bushings are
replaced by reamer bushings and each hole is finished by ream-
ing. The small hole c, Fig. 4, is drilled in the end of the cast-
ing by simply placing the jig on end as shown at B, Fig. 5.
Box jigs which have to be placed in more than one position
for drilling the different holes are usually provided with feet
or extensions, as shown, which are accurately finished to align
the guide bushings properly with the drill. These feet extend
beyond any clamping screws, bolts, or bushings which may
protrude from the sides of the jigs, and provide a solid support.
When inserting work in a jig, care should be taken to remove
all chips which might have fallen upon those surfaces against
which the work is clamped and which determine its location.

Still another jig of the box type, which is quite similar to
the one shown at A, Fig. 4, but is arranged differently, owing
to the shape of the work and location of the holes, is shown
at B in the same illustration. The work has three holes in
the base h, and a hole at i which is at an angle of 5 degrees
with the base. The three holes are drilled with the jig stand-
ing on the opposite end y, and the angular hole is drilled while
the jig rests on the four feet k, the ends of which are at such an
angle with the jig body that the guide bushing for hole i is prop-
erly aligned with the drill. The casting is located in this jig
by the inner ends of the two guide bushings w and the bushing
o and also by two locating screws p and a side locating screw q.
Adjustable screws t and t\ in the cover hold the casting down,
and it is held laterally by the two knurled thumb-screws u
and v. If an attempt were made to drill this particular part
without a jig (as would be done if only a few castings were

JIG DESIGN 19

needed) it would have to be set with considerable care, provided
the angle between hole i and those in the base had to be at
all accurate, and it would be rather difficult to drill a number
of these castings and have them all duplicates. By the use of
a jig, however, designed for drilling this particular casting,
the relative positions of the holes in any number of parts are
practically the same and the work can be done much more
quickly than would be possible if it were held to the drill-press
table by ordinary clamping appliances. Various designs of jigs
will be described in Chapter VII.

Details of Jig Design. — The general principles of the design
and use of jigs have been explained. The details of jig design
will now be considered. Generally speaking, the most im-
portant parts of a jig are the guide bushings for the drills and
other tools, the clamping devices, and the locating points,
against which the work is placed to insure an accurate posi-
tion in the jig. The guides for the cutting tools in a drill jig
take the form of concentric steel bushings, which are placed in
the jig body in proper positions.

The drill bushings are generally made of tool steel, hardened
and lapped, and, where convenient, should be ground inside
and out. They should also be long enough to support the
drill on each side regardless of the fluting, and they should be
so located that the lower end of the bushings will stop about
the same distance above the work as the diameter of the drill,
so that chips will clear the bushings readily. Where holes are
drilled on the side of a convex or a concave surface, the end of
the bushing must be cut on a bevel and come closer to the part
being drilled, to insure the drill having adequate support while
starting into the work. The bushings should have heads of
sufficient diameter. Long bushings should be relieved by in-
creasing the hole diameter at the upper end. The lower end
of the bushing should have its edges rounded, in order to permit
some of the chips being shed from the drill easily, instead of
all of them being forced up through the bushing. It is also
good practice to cut a groove under the head for clearance for
the wheel when grinding the bushing on the outside. A com-

20 JIG DESIGN

plete treatise covering dimensions and design is given in the
chapter on "Jig Bushings."

In order to hold the work rigidly in the jig, so that it may
be held against the locating points while the cutting tools
operate upon the work, jigs and fixtures are provided with
clamping devices. Sometimes a clamping device serves the
purpose of holding the jig to the work, in a case where the
work is a very large piece and the jig is attached to the work
in some suitable way. The purpose of the clamping device,
however, remains the same, namely, that of preventing any
shifting of the guiding bushings while the operation on the
work is performed. The clamping device should always be an
integral part of the jig body in order to prevent its getting lost.
Different types of clamping devices are shown and described
in the chapter on "Jig Clamping Devices. "

The locating points may consist of screws, pins, finished
pads, bosses, ends of bushings, seats, or lugs cast solid with
the jig body, etc. The various types used are described in
detail in the chapter on "Locating Points and Adjustable
Stops."

CHAPTER II
DESIGN OF OPEN DRILL JIGS

To give any rational rules or methods for the design of drill
jigs would be almost impossible, as almost every jig must be
designed in a somewhat different way from every other jig, to
suit and conform to the requirements of the work. All that can
be done is to lay down the principles. The main principles for
jigs as well as fixtures were treated at length in Chapter I.
It is proposed in the present chapter to dwell more in detail on
the carrying out of the actual work of designing jigs.

Jig Drawings. — Before making any attempt to put the lay-
out of the jig on paper, the designer should carefully consider
what the jig will be required to do, the limits of accuracy, etc.,
and to form, in his imagination, a certain idea of the kind of a
jig that would be suitable for the purpose. In doing so, if a
model or sample of the work to be made is at hand, it will be
found to be a great help to study the actual model. If the draw-
ing, as is most often the case, is the only thing that is at hand,
then the outline of the work should be drawn in red (or other
colored) ink on the drawing paper, on which the jig is subse-
quently to be laid out, and the jig built up, so to speak, around
this outline. The designing of the jig will be greatly simplified
by doing this, as the relation between the work and the jig will
always be plainly before the designer, and it will be more easily
decided where the locating points and clamping arrangements
may be properly placed. When drawing and projecting the
different views of the jig on the paper, the red outline of the work
will not in any way interfere, and when the jig is made from the
drawing, the red lines are simply ignored, except to the extent
to which the outline of the pieces may help the toolmaker to
understand the drawing and the purpose of certain locating points
and clamping devices.

22 JIG DESIGN

If possible, the jig should be drawn full size, as it is a great
deal easier to obtain the correct proportions when so doing.
Of course, in many cases, it will be impossible to draw the jigs
full size. In such cases the only thing to do is to draw them to
the largest possible regular scale. Every jig draftsman should
be supplied with a set of blueprints containing dimensions of
standard screws, bolts, nuts, thumb-screws, washers, wing-nuts,
sliding points, drills, counterbores, reamers, bushings, etc.; in
short, with blueprints giving dimensions of all parts that are used
in the construction of jigs, and which are, or can be, standardized.
It should be required of every designer and draftsman that he use
these standards to the largest possible extent, so as to bring the
cost of jigs down to as low a figure as possible.

It is highly desirable, for the obtaining of best results, that,
before starting on the drawing, the draftsman who is to lay out
the jig should consult the foreman who is actually going to use
the jig. Oftentimes this man will be able to supply the best idea
for the making of the jig or tool. The combined experience of
the draftsman and the foreman will generally produce a much
better tool than could either of them alone.

As a jig drawing, in most cases, is only used once, or at most
only a very few times, it is not advisable to make a tracing or
blueprint from the drawing, but, as a rule, the pencil drawing itself
may be used to advantage. If, however, it is given out in the
shop directly as it comes from the drawing-board, it is likely
to become soiled, so that, after a while, it would be impossible
to make out the meaning of the views shown on it. For this
reason jig drawings should be made on heavy paper, preferably
of brown color, which is not as quickly soiled as white paper;
and in order to prevent the drawing from being torn, it should
be mounted on strawboard, and held down along the edges by
thin wooden strips, nailed to the board. It is also desirable to
cover the drawings with a thin coat of shellac before they are
sent out into the shop. When this is done, dirt and black spots
may be washed off directly; and the shellac itself may be washed
off by wood alcohol, when the drawing is returned to the draft-
ing-room. The drawing, after having been cleaned, is then

OPEN DRILL JIGS 23

detached from the strawboard, which may be used over and over
again. The drawing is, of course, filed away according to the
drafting-room system. The most advantageous sizes for jig
drawings for from medium to heavy work are about as follows:

1. Full-size sheet, 40 X 27^ inches.

2. Half-size sheet, 27^ X 20 inches.

3. Quarter-size sheet, 20 X 13! inches.

4. Eighth-size sheet, i3f X 10 inches.

Of course, these sizes will vary in different shops, and in many
cases, particularly when the tool-designing department and the
regular drafting-room are combined as one drafting department,
the jig drawings should be of the same regular sizes as the ordi-
nary machine drawings.

It is common practice in a great many shops to make no de-
tailed drawings of jigs, but simply to draw a sufficient number of
views and sections, and to dimension the different parts directly
on the assembly drawings. In cases where the jig drawings are
complicated, and where they are covered with a large number
of dimensions which make it hard to read the drawing and to see
the outlines of the jig body itself, it has proved a great help to
trace the outlines of the jig body, and of such portions as are
made of cast iron, on tracing paper, omitting all loose parts, and
simply putting on the necessary dimensions for making the pat-
terns. A blueprint is then made from this paper tracing, and is
sent to the patternmaker, who will find the drawing less of a
puzzle, and who will need to spend far less time to understand
how the pattern actually looks. It is, however, good policy to
detail jig drawings completely, the same as other machine de-
tails.

When jigs are made for pieces of work which require a great
many operations to be carried out with the same jig, and where
a great number of different bushings, different sizes of drills,
reamers, counterbores, etc., are used, a special operation sheet
should be provided, which should be delivered to the man using
the jig, together with the jig itself. This enables him to use the
jig to best advantage. On this sheet should be marked the order
in which the various operations are to be performed and the

JIG DESIGN

L-L1L.

L-.-.-1

OPEN DRILL JIGS 25

tools and bushings which are to be used. The bushings should
be numbered or marked in some way so as to facilitate the selec-
tion of the correct bushing for the particular tool with which it
is used. If this system is put in force and used for simpler
classes of jigs also, the operator will need few or no instructions
from the foreman, outside of this operation sheet.

Designing Open Jigs. — The present chapter will be de-
voted to explaining and illustrating the application of the prin-
ciples previously outlined, to the simplest and most common
design of drill jig — the open jig. Assume that the drill jig is
to be designed for a piece of work, as shown in Fig. i. Con-
sideration must first be given to the size of the piece, to the finish
given to the piece previous to the drilling operation, the accu-
racy required as regards the relation of one hole to the other,
and in regard to the surfaces of the piece itself. The number
of duplicate pieces to be drilled must also be considered, and,
in some cases, the material.

The simplest kind of drill jig that could be used for the case
taken as an example would be the one illustrated in Fig. 2,
which simply consists of a flat plate of uniform thickness of the
same outline as the piece to be drilled, and provided with holes
for guiding the drill. Such a jig would be termed a jig-plate.
For small pieces, the jig-plate would be made of machine steel
and casehardened, or from tool steel and hardened. For larger
work, a machine-steel plate can also be used, but in order to
avoid the difficulties which naturally would arise from harden-
ing a large plate, the holes are simply bored larger than the
required size of drill, and are provided with lining bushings to
guide the drill, as shown in Fig. 3. It would not be necessary,
however, to have the jig-plate made from steel, for large work,
as a cast-iron plate provided with tool steel or machine-steel
guiding bushings would answer the purpose just as well, and
be much cheaper. The thickness of the jig-plate varies accord-
ing to the size of the holes to be drilled and the size of the plate
itself.

The holes in the jig in Fig. 2 and in the bushings in the jig in
Fig. 3 are made the same size as the hole to be drilled in the work,

26 JIG DESIGN

with proper clearance for the cutting tools. If the size and loca-
tion of the holes to be drilled are not very important as regards
accuracy, it is sufficient to simply drill through the work with a
full-sized drill guided by the jig-plate, but when a nice, smooth,
standard-sized hole is required, the holes in the work must be
reamed. The hole is first spotted by a spotting drill, which is
of exactly the same size as the reamer used for finishing, and
which nicely fits the hole in the jig-plate or bushing. Then a
so-called reamer drill, which is o.oio inch, or less, smaller in
diameter than the reamer, is put through, leaving only a slight
amount of stock for the reamer to remove, thereby obtaining a
very satisfactory hole. Sometimes a separate loose bushing is used
for each one of these operations, but this is expensive and also
unnecessary, as the method described gives equally good results.

By using the rose reaming method very good results will also
be obtained. In this case two loose bushings besides the lining
bushing will be used. These bushings are described and tabu-
lated in a following chapter. The drill preceding the lose
chucking reamer is TV inch smaller than the size of the hole.
This drill is first put through the work, a loose drill bushing
made of steel being used for guiding the drill. Then the rose
chucking reamer is employed, using, if the hole in the jig be
large, a loose bushing made of cast iron.

When dimensioning the jig on the drawing, dimensions should
always be given from two finished surfaces of the jig to the
center of the holes, or at least to the more important ones. In
regard to the holes, it is not sufficient to give only the right
angle dimensions, a, 5, c, and d, etc., Fig. 2, but the radii between
the various holes must also be given. If there are more than
two holes, the radii should always be given between the nearest
holes and also between the holes that bear a certain relation
to one another, as, for instance, between centers of shafts carry-
ing meshing gears, sprockets, etc. This will prove a great help
to the toolmaker. In the case under consideration, the dimen-
sions ought to be given from two finished sides of the work to
the centers of the holes, and also the dimension between the
centers of the holes to be drilled.

OPEN DRILL JIGS

When using a simple jig, made as outlined in Figs. 2 and 3,
this jig is simply laid down flat on the work and held against it
by a C-clamp, a wooden clamp, or, if convenient, held right on
the drill-press table by means of a strap or clamp, as shown in
Fig. 4. Here two pieces of the work are shown beneath the jig-
plate, both being drilled at one time.

Improving the Simple Form of Jig. — The first improvement
that could be made on the jig shown in Fig. 3 would be the plac-
ing of locating points in the jig-plate in the form of pins, as shown
in Fig. 5, in which the dotted lines represent the outline of the
work. The plate need not necessarily have the shape shown in

Fig. 7. Simple Jig with Locating Screws Holding the
Work in Place

Fig. 5, but may have the appearance shown in Fig. 6, according
to the conditions.

The adding of the locating points will, of course, increase the
cost of the jig, but the amount of time saved in using the jig
will undoubtedly make up for the added expense of the jig,
provided a fair number of pieces is to be drilled; besides a great
advantage is gained in that the holes will always be located in
the same relation to the two sides resting against the locating
pins on all the pieces drilled. The locating pins are flattened
off to a depth of TV inch from the outside circumference, and
dimensions should be given from the flat to the center of the pin

28 JIG DESIGN

holes and to the center of the nearest or the most important of
the holes to be drilled in the jig. The same strapping or clamp-
ing arrangements for the jig and work, as mentioned for the
simpler form of jig, may be employed.

Improving the Jig by Adding Locating Screws. — The next
step toward improving the jig under consideration would be to
provide the jig with locating screws, as shown in Fig. 7. By
the addition of these, the locating arrangements of the jig be-
come complete, and the piece of work will be prevented from
shifting or moving sideways. These locating screws are placed
so that the clamping points come as nearly opposite to some
bearing points on the work as possible. In order to provide for
locating set-screws in our present jig, three lugs or projections
A are added which hold the set-screws. If possible the set-screw
lugs should not reach above the surface of the work, which
should rest on the drill-press table when drilling the holes.

The present case illustrates the difficulty of giving exact rules
for jig design. Two set-screws are used on the long side of the
work, but in a case like this, where the piece is comparatively
short and stiff, one lug and set-screw, as indicated by the dotted
lines at B in Fig. 7, would be fully sufficient. The strain of the
set-screw placed right between the two locating pins will not be
great enough to spring the piece out of shape. When the work
is long and narrow, two set-screws are required on the long side,
but, in the case illustrated, two lugs would be considered a waste-
ful design.

Providing Clamps and Feet for the Jig. — The means by which
the work has been clamped or strapped to the jig when drilling
in the drill press (see Fig. 4) have not been integral parts of the
jig in the simple types shown. If clamping arrangements that
are integral parts of the jig are to be added, the next improve-
ment would be to add four legs in order to raise the jig-plate
enough above the surface of the drill-press table to get the re-
quired space for such clamping arrangements. The completed
jig of the best design for rapid manipulation and duplicate work
would then have the appearance shown in Fig. 8. The jig here
is provided with a handle cast integral with the jig body, and

OPEN DRILL JIGS

with a clamping strap which can be pulled back for removing
and inserting the work. Instead of having the legs solid with
the jig, as shown in Fig. 8, loose legs, screwed in place, are some-
times used, as shown in Fig. 9.

These legs are round and provided with a shoulder A, prevent-
ing them from screwing into the jig-plate. A headless screw or
pin through the edge of the circumference of the threads at the
top prevents the studs from becoming loose. These loose legs
are usually made of machine steel or tool steel, the bottom end

Standard Jig Feet

9ia

5/i2

'Me
%

Screws for Jig Feet

o. 160
o. 191
0.213
0.233
0.256

O.IIO

0.123

0.137

0.150
0.164

0.299

0-343
0.386
0.426

9xi2

0.192
0.219
0.246
0.273

being hardened and then ground and lapped, so that all four
legs are of the same length. It is the practice of many tool-
makers not to thread the legs into the jig body, but simply to
provide a plain surface on the end of the leg, which enters into
the jig-plate, and is driven into place. This is much easier, and
there is no reason why, for almost all kinds of work, jigs provided
with legs attached in this manner should not be equally durable.

Jig feet are also made of the form shown in the accompanying
table, where a separate screw is used for holding the jig feet to
the jig body.

When jigs are made of machine or tool steel, and feet are

3o'

JIG DESIGN

OPEN DRILL JIGS 31

required, the only way to provide them is to insert loose feet.
In the case of cast-iron jigs, however, solid legs cast in place are
preferable. The solid legs cast in place generally have the appear-
ance shown in the upper right-hand corner of Fig. 8. The two
webs of the leg form a right angle, which, for all practical pur-
poses, makes the leg fully as strong as if it were solid. The
leg is tapered 15 degrees, as a rule, as shown in the engraving,
but this may be varied according to conditions. The thickness
of the leg varies according to the size of the jig, the weight of the
work, and the pressure of the cutting tools, and depends also
upon the length of the leg. The length b on top is generally
made one and one-half times a. As an indication of the size
of the legs required, it may be said that for smaller jigs, up to
jigs with a face area of 6 square inches, the dimension a may be
made from -£$ to f inch; for medium-sized jigs, J to f inch; for
larger-sized jigs, f to i| inch; but, of course, these dimensions
are simply indications of the required dimensions. As to the
length of the legs, the governing condition, evidently, is that
they must be long enough to reach below the lowest part of the
work and the clamping arrangement, as clearly indicated in the
design in Fig. 8.

If a jig is to be used in a multiple-spindle drill, it should be
designed a great deal stronger than it is ordinarily designed when
used for drilling one hole at a time. This is especially true if
there is a large number of holes to drill simultaneously. It is
evident that the pressure upon the jig in a multiple-spindle drill
is as many times greater than the pressure in a common drill
press as the number of drills in operation at once.

Referring again to Fig. 8, attention should be called to the
small lugs A on the sides of the jig body which are cast in place
for laying out and planing purposes. The handle should be
made about 4 inches long, which permits a fairly good grip by
the hand. The design of the jig shown is simple, and fills all
requirements necessary for producing work quickly and accu-
rately; at the same time, it is strongly and rigidly designed.
Locating points of a different kind from those shown can, of
course, be used; and the requirements may be such that adjust-

JIG DESIGN

able locating points, as described in a following chapter, may be
required. A more quick-acting, but, at the same time, a far more
complicated clamping arrangement might be used, but the
question is whether the added increase in the rapidity of manipu-
lation offsets the expense thus incurred.

A question which the designer should always ask himself is:
Can more than one piece be drilled at one time? In the present
case, the locating pins can be made longer, or, if there is a locat-
ing wall, it can be made higher, the legs of the jig can be made
longer, and the screw holding the clamp can also be increased in
length. If the pieces of work are thick enough, set-screws for

Fig. 9. Legs Screwed into Jig Body

holding the work against the locating pins can be placed in a
vertical line, or if the pieces are narrow, they can be placed
diagonally, so as to gain space. If the pieces are very thin,
the locating might be a more difficult proposition. If they are
made of a uniform width, they may simply be put in the slot
in the bottom of the jig, as shown in the lower right-hand corner
of Fig. 8, or if a jig on the principles of the one shown to the left
is used, they might be located sideways by a wedge, as shown in
Fig. 10. A couple of lugs A would then be added to hold the
wedge in place and take the thrust. In both cases the pieces
must be pushed up in place endways by hand. If the pieces are
not of exactly uniform size and it is desired to drill a number

OPEN DRILL JIGS

at a time, they must be pushed up against the locating pins by
hand from two sides, and the clamping strap must be depended
upon to clamp them down against the pressure of the cut, and
at the same time prevent them from moving side or endways.
If the accuracy of the location of the holes is important, but
one piece at a time should be drilled.

Examples of Open Drill Jigs. — A typical example of an open
drill jig, very similar to the one just developed and explained,
is shown in Fig. n. The work is located against the three locat-
ing pins A, and held in place against these pins by the three
set-screws B. The three straps C hold the work securely against

Fig. 10. Jig with Wedge for Holding the Work

the finished pad, in the bottom of the jig. These clamps are so
placed that when the work has been drilled and the clamp screws
loosened, the clamps will swing around a quarter of a turn, allow-
ing the work to be lifted directly from the jig and a new piece of
work inserted; then the clamps are again turned around into the
clamping position, and the screws tightened. These straps are
integral parts of the jig; at the same time, they are quickly and
easily manipulated, and do not interfere with the rapid removal
and insertion of the work. The strength and rigidity of the feet
in proportion to the jig should be noted, this strength being ob-
tained by giving proper shape to the feet, without using an un-
necessary quantity of metal.

The jig in Fig. 1 1 is also designed to accommodate the compo-
nent part of the work when it is to be drilled. When this is done,
the work is held on the back side of the jig, shown in Fig. 12.

34 JIG DESIGN

This side is also provided with feet, and has a finished pad against
which the work is held. The locating pins extend clear through
the central portion of the jig body, and, consequently, will locate
the component part of the work in exactly the same position as
the piece of work drilled on the front side of the jig. The same
clamping straps are used, the screws being simply put in from
the opposite side into the same tapped holes as are used when
clamping on the front side of the jig. The four holes D are
guide holes for drilling the screw holes in the work, these being
drilled the body size of the bolt in one part, and the tap drill size

Fig. ii. Example of Open Drill Jig. View showing Front Side

in the component part. The lining bushing in the holes D serves
as a drill bushing for drilling the body size holes. The loose
bushing E, Fig. n, is used when drilling the tap holes in the
component part, the inside diameter of this bushing being the
tap drill size, and the outside diameter a good fit in the lining
bushing. The two holes F, Fig. 12, are provided with drill
bushings and serve as guides when drilling the dowel pin holes,
which are drilled below size, leaving about o.oio inch, and are
reamed out after the two component parts of the work are put
together. The two holes shown in the middle of the jig in Fig.
n, which are provided with lining bushings, and also with
loose bushings, as shown inserted in Fig. 12, may be used for

OPEN DRILL JIGS 35

drilling and reaming the bearing holes for the shafts passing
through the work. In this particular case, however, they are
used only for rough-drilling the holes, to allow the boring-bars
to pass through when finishing the work by boring in a special
boring jig, after the two parts of the work have been screwed
together.

The large bushings shown beside the jig in Fig. n are the
loose bushings shown in place in Fig. 12. It will be noted that
the bushings are provided with dogs for easy removal, as ex-
plained in a following chapter. As the central portion of the

Fig. 12. Rear View of Drill Jig shown in Fig. n

jig body is rather thin, it will be seen from Fig. 12 that the bosses
for the central holes project outside of the jig body in order to
give a long enough bearing to the bushings. This, of course,
can be done only when such a projection does not interfere with
the work. The bosses, in this particular case, also serve another
purpose. They make the jig " fool-proof ," because the pieces
drilled on the side of the jig shown in Fig. n cannot be put on
the side shown in Fig. 12, the bosses preventing the piece from
being placed in position in the jig.

Attention should be called to the simplicity of the design of
this jig. It simply consists of a cast-iron plate, with finished
seats, and feet projecting far enough to reach below the work

JIG DESIGN

when drilling, three dowel pins, set-screws for bringing the work
up against the dowel pins, three clamps, and the necessary
bushings. The heads of all the set-screws and bolts should, if
possible, be made the same size, so that the same wrench may be
used for tightening and unscrewing all of them. It can also be
plainly seen from the halftones that there are no unnecessarily
finished surfaces on the jig, a matter which is highly important
in economical production of tools.

Another example of an open drill jig, similar in design to the
one just described, is shown in Fig. 13. The work to be drilled

Fig. 13. Drill Jig Used for Drilling Work shown to the Right

in this jig is shown at A and B at the right-hand side of the jig.
In this case, the work is located from the half-circular ends.
The pieces A and B are component parts and, when finished, are
screwed together. The piece A is located against three dowel
pins, and pushed against them by set-screws C, and held in posi-
tion by three clamping straps, as shown in Fig. 14. In this case,
the straps are provided with oblong slots as indicated, and when
the clamp screws are loosened the clamps are simply pulled
backward, permitting the insertion and removal of the work
without interference. It would improve this clamping arrange-
ment to place a stiff helical spring around the screws under each
strap, so that the straps would be prevented from falling down to

OPEN DRILL JIGS 37

the bottom of the jig when the work was removed. At the same
time this would prevent the straps from swiveling around the
screws when not clamped.

In Fig. 15, the part B in Fig. 13 is shown clamped in position
for drilling, the opposite side of the jig being used for this pur-
pose. In jig design of this kind it is necessary to provide some
means so that the parts A and B will be placed each on the
correct side of the jig, or, as mentioned, the jig should be made
" fool-proof. " In the present case, the parts cannot be exchanged
and placed on the wrong side, because the cover or guard B can-
not be held by the three straps shown in Fig. 14, as the screws

Fig. 14. Drill Jig shown in Fig. 13 with Work in Place

for the straps are not long enough. On the other hand, the
piece A could not be placed on the side shown in Fig. 15, because
the long bolt and strap used for clamping on this side would
interfere with the work.

It may appear to be a fault in design that three straps are used
to fasten the piece A in place, and only one is employed for hold-
ing piece B. This difference in clamping arrangement, however,
is due to the different number and the different sizes of holes to
be drilled in the different pieces. The holes in the piece A are
larger and the number of holes is greater, and a heavier clamping
arrangement is, therefore, required, inasmuch as the thrust on

3 8 JIG DESIGN

the former is correspondingly greater, the multiple-spindle drill
being used for drilling the holes. If each hole were drilled and
reamed individually, the design of the jig could have been com-
paratively lighter.

In the design shown, the locating of each piece individually
in any but the right way is also taken care of. The piece A,
which is shown in place in the jig, Fig. 14, could not be swung
around into another position, because the strap and screw at E
would interfere. For the same reason, the cover or guard B
could not be located except in the right way. As shown in Fig.

Fig. 15. Rear View of Drill Jig shown in Fig. 13, with Cover
to be Drilled in Place

15, the strap and screw would have to be detached from the jig
in order to get the cover in place, if it were turned around. The
locating pins for the work pass clear through the body of the jig,
and are used for locating both pieces. The pieces are located
diagonally in the jig, because, by doing so, it is possible to make
the outside dimensions of the jig smaller. In this particular
case the parts are located on the machine to which they belong,
in a diagonal direction, so that the additional advantage is gained
of being able to use the same dimensions for locating the jig
holes as are used on the drawing for the machine details them-
selves. This also tends to eliminate mistakes in making the jigs.
Sometimes, when more or less complicated mechanisms are

OPEN DRILL JIGS 39

composed of several parts fitted together and working in relation
to each other, as, for instance, friction clutches, one jig may be
made to serve for drilling all the individual parts, by the addition
of a few extra parts applied to the jig when different details of
the work are being drilled. In Figs. 16, 17, and 18, such a case
is illustrated. The pieces A, B, and C, in Fig. 16, are component
parts of a friction clutch, and the jig in which these parts are
being drilled is shown in the same figure, to the left. Suppose
now that the friction expansion ring A is to be drilled. The jig
is bored out to fit the ring before it is split and when it is only

Fig. 1 6. Drill Jig for Parts of Friction Clutches shown at the Right

rough-turned, leaving a certain number of thousandths of an
inch for finishing. The piece is located, as shown in Fig. 17,
against the steel block D entering into the groove in the ring, and
is then held by three hook-bolts, which simply are swung around
when the ring is inserted or removed. The hook-bolts are
tightened by nuts on the back side of the jig. Three holes
marked E in Fig. 17 are drilled simultaneously in the multiple-
spindle drill, and the fourth hole F (see Fig. 16) is drilled by
turning the jig on the side. The steel block D, Fig. 17, is hard-
ened, and has a hole to guide the drill when passing through into
the other side of the slot in the ring. The block is held in place
by two screws and two dowel pins.

40 JIG DESIGN

When drilling the holes in the lugs in the friction sleeve B,
Fig. 1 6, the block D and the hook-bolts are removed. It may
be mentioned here, although it is a small matter, that these
parts should be tied together when removed, and there should
be a specified place where all the parts belonging to a particular
jig should be kept when not in use. The friction sleeve B fits
over the collar G} Fig. 180 This collar is an extra piece, belong-
ing to the jig, and used only when drilling the friction sleeve;
it should be marked with instructions for what purpose it is
used. The collar G fits over the projecting finished part H in

Fig. 17. Drill Jig shown in Fig. 16, with One of the Pieces in Place

the center of the jig, and is located in its right position by the
key ways shown. The keyway in the friction sleeve B} which
must be cut and placed in the right relation to the projecting
lugs before the piece can be drilled, locates the sleeve on the
collar G} which is provided with a corresponding keyway. A
flange on the collar G} as shown more plainly at L in Fig. 18,
locates the friction sleeve at the right distance from the bottom
of the jig, so that the holes will have a proper location sideways.
Two collars, G and L, are used for the same piece B, this being
necessary because the holes M and M in the projecting lugs
shown in Fig. 16 are not placed in the same relation to the sides
of the friction sleeve. The collars are marked to avoid mis-
takes, and corresponding marks on the jig provided so as to

OPEN DRILL JIGS

assure proper location. The friction sleeve is clamped in place
by a strap which, in this case, does not form an integral part of
the jig. This arrangement, however, is cheaper than it would
have been to carry up two small projections on two sides of the
jig and employ a swinging leaf and an eye-bolt, or some arrange-
ment of this kind. Besides, the strap is rather large, and could
not easily get lost. The jig necessarily has a number of loose
parts, on account of being designed to accommodate different
details of the friction clutch.

The friction disks C, in Fig. 16, when drilled, fit directly over
the projecting finished part H of the jig, and are located on this

Fig. 18. Drill Jig shown in Fig. 16 used for Drilling Friction Sleeve

projection by a square key. The work is brought up against
the bottom of the jig and held in this position by the strap shown
in Fig. 1 8 for holding the friction sleeve. The bushings of
different sizes shown in Fig. 18 are used for drilling the different
sized holes in the different parts.

In all the various types of drill jigs described, the thrust of
the cutting tools is taken by the clamping arrangement. In
many cases, however, no actual clamping arrangements are
used, but the work itself takes the thrust of the cutting tools,
and the locating means are depended upon to hold the piece or
jig in the right position when performing the drilling operation.

42 JIG DESIGN

It may be well to add that loose bushings ought to be marked
with the size and kind of cutting tool for which they are intended;
and the corresponding place in the jig body where they are to be
used should be marked so that the right bushing can easily be
placed in the right position.

A few more examples of open drill jig designs of various types
may prove instructive. In Fig. 19 are shown two views of a jig
for drilling two holes through the rim of a handwheel. To the
left is shown the jig itself and to the right the jig with the hand-

Fig. 19. Drill Jig for Holes in Rim of Handwheel

wheel mounted in place, ready for drilling. As shown, the hand-
wheel is located on a stud through its bore, and clamped to the
jig by passing a bolt through the stud, this bolt being provided
with a split washer on the end. The split washer permits the
easy removal of the handwheel when drilled, and the putting in
place of another handwheel without loss of time. The hand-
wheel is located by two set-screws B passing through two lugs
projecting on each side of a spoke in the handwheel, the set-
screws B holding the handwheel in position, while being drilled,
by clamping against the sides of the spoke. The jig is fastened
on the edge of the drill-press table, in a manner similar to that
indicated in the illustration, so that the table does not interfere

OPEN DRILL JIGS

with the wheel. The vertical hole, with the drill guided by
bushing G, is now drilled in all the handwheels, this hole being
drilled into a lug in the spoke held by the two set-screws B.
When this hole is drilled, the jig is moved over to a horizontal
drilling machine, and the hole D is drilled in all the handwheels,
the jig being clamped to the table of this machine in a manner
similar to that on the drill press.

Fig. 20. Miscellaneous Examples of Open Drill Jigs

In Fig. 20, at A, an open drill jig of a type similar to those
shown in Figs, n and 13, is shown. This jig, however, is pro-
vided with a V-block locating arrangement. An objectionable
feature of this jig is that the one clamping strap is placed in the
center of the piece to be drilled. Should this piece be slender,
it may cause it to bend, as there is no bearing surface under the

44 JIG DESIGN

work, at the place where the clamp is located, for taking the
thrust of the clamping pressure.

At B and C in the same illustration are shown the front and
back views of a drill jig, where the front side B is used for drill-
ing a small piece located and held in the jig as usual; and the
back side C, which is not provided with feet, is located and applied
directly on the work itself in the place where the loose piece is
to be fastened, the work in this case being so large that it sup-
ports the jig, instead of the jig supporting the work.

At D in the same illustration is shown a jig for locating work
by means of a tongue E. This tongue fits into a corresponding
slot in the work. This means for locating the work was referred
to more completely in connection with locating devices. Finally,
at F, is shown a jig where the work is located by a slot G in the
jig body, into which a corresponding tongue in the work fits.

CHAPTER HI
DESIGN OF CLOSED OR BOX JIGS

In the preceding chapter, the subject of the design of open
drill jigs has been dealt with. In the present chapter it is pro-
posed to outline the development of the design of closed or box

jigs-

Assume that the holes in a piece of work, as shown in Fig. i,
are to be drilled. Holes A are drilled straight through the work,
while holes B and C are so-called " blind holes," drilled into the
work from the opposite sides. As these holes must not be drilled
through, it is evident that the work must be drilled from two
sides, and the guiding bushings for the two blind holes must
be put in opposite sides of the jig. The simplest form of jig
for this work is shown in Fig. 2. The piece of work D is located
between the two plates E, which form the jig, and which, if the
jig is small, are made of machine steel and casehardened. If
the jig is large these plates are made of cast iron. The work D
is simply located by the outlines of the plates, which are made
to the same dimensions, as regards width, as the work itself.
The plates are held in position in relation to each other by the
guiding dowel pins F. These pins are driven into the lower
plate and have a sliding fit in the upper one. In some cases,
blocks or lugs on one plate would be used to fit into a slot in the
other plate instead of pins. These minor changes, of course,
depend upon the nature of the work, the principle involved being
that some means must be provided to prevent the two plates
from shifting in relation to each other while drilling. The
whole device is finally held together by clamps of suitable form.
The holes A may be drilled from either side of the jig, as they
pass clear through the work, and the guides for the drills for
these holes may, therefore, be placed in either plate. Opposite
the bushings in either plate a hole is drilled in the other plate

JIG DESIGN

for clearance for the drill when passing through, and for the
escape of the chips.

The two plates should be marked with necessary general in-
formation regarding the tools to be used, the position of the plates,
etc., to prevent mistakes by the operator. It is also an advan-
tage, not to say a necessity, to use some kind of connection be-
tween the plates in order to avoid such mistakes as, for instance,
the placing of the upper plate in a reversed position, the wrong
pins entering into the dowel pin holes. This, of course, would
locate the holes in a faulty position. Besides, if the upper plate
be entirely loose from the lower, it is likely to drop off when the
jig is stored, and get lost. Some means of holding the two parts

tfTt

Fig. i. Work to be Drilled

together, even when not in use, or when not clamped down on
the work, should therefore be provided. Such a means is em-
ployed in Fig. 2, where the screw G enters into the guiding dowel
pin at the left and holds the upper plate in place. A pin H,
fitting into an elongated slot in the dowel pin, as shown at the
left, could also be used instead of the screw. The design shown
presents the very simplest form of box jig, consisting, as it does,
of only two plates for holding the necessary guiding arrange-
ments, and two pins or other means for locating the plates in
relation to each other.

In manufacturing, where a great number of duplicate parts
would be encountered, a jig designed in the simple manner shown
in Fig. 2 would, however, be wholly inadequate. The simplest

BOX JIGS

form of a jig that would be used in such a case would be one in
which some kind of locating means is employed, as indicated in
Fig. 3, where three pins are provided, two along the side of the
work and one for the end of the work, against which the work

Fig. 2. Simple Form of Closed Jig for Drilling Work
shown in Fig. i

may be pushed prior to the clamping together of the two jig-
plates. In this illustration, the jig bushings are not shown in
the elevation and end view, in order to avoid confusion of lines.
The next improvement to which this jig would be subjected would

Fig. 3. Locating Pins added to Jig

be the adding of walls at the end of the jig and the screwing
together of the upper and lower plate, the result being a jig as
shown in Fig. 4. This design presents a more advanced style of
closed jig — a type which could be recommended for manufac-
turing purposes. While the same fundamental principles are

JIG DESIGN

still in evidence, this jig embodies most of the requirements
necessary for rapid work. This design provides for integral
clamping means within the jig itself, provided, in this case, by
the screws /. The upper plate K is fastened to the walls of the
lower plate L by four or more screws M and two dowel pins N.
The cover K could also be put on, as shown in Fig. 5, by making
the two parts a good fit at 0, one piece being tongued into the
other. This gives greater rigidity to the jig. In this jig, also,
solid locating lugs F are used instead of pins.

Referring again to Fig. 4, by providing a swinging arm P with
a set-screw Q, the work can be taken out and can be inserted

Fig. 4. Jig Suitable for Manufacturing Purposes

from the side of the jig, which will save making any provisions
for taking off or putting on the top cover for every piece being
drilled. If there is enough clearance between the top cover and
the piece being drilled, the screw Q could, of course, be mounted
in a solid lug, but it would not be advantageous to have so large
a space between the top plate and the work, as the drill would
have to extend unguided for some distance before it would reach
the work. The set-screws Q and U hold the work against the
locating points, and the set-screws / on the top of the jig, pre-
viously referred to, hold the work down on the finished pad R
on the bottom plate. These screws also take the thrust when
the hole C is drilled from the bottom side. It is immaterial on
which side the bushings for guiding the drills for the two holes
A are placed, but by placing them in the cover rather than in

BOX JIGS

the bottom plate, three out of the four bushings will be located
in the top part, and when using a multiple-spindle drill, the face
R will take the greater thrust, which is better than to place the
thrust on the binding screws /. In the designs in Figs. 4 and
5 the whole top and bottom face of the jig must be finished, or a
strip marked/ in Fig. 6, at both ends of the top and bottom sur-
faces, must be provided, so that it can be finished, and the jig
placed on parallels D as illustrated.

While the jig itself, developed so far, possesses most of the
necessary points for rapid production and accurate work, the

J L

Fig. 5. Alternative Design of Jig shown in Fig. 4

use of parallels, as indicated in Fig. 6, for supporting the jig
when turned over so that the screw-heads of the clamping screws
point downward, is unsatisfactory. Therefore, by adding feet
to the jig, as shown in Fig. 7, the handling of the jig will be a
great deal more convenient. The adding of the protruding
handle 5 will still further increase the convenience of using the
jig. The design in Fig. 7 also presents an improvement over
that in Fig. 4, in that, besides the adding of feet and handle, the
leaf or strap E is used for holding screw Q instead of the arm P.
This latter is more apt to bend if not very heavy, and would
then bring the set-screw in an angle upwards, which would have
a tendency to tilt the work. The strap can be more safely relied
upon to clamp the work squarely. Two set-screws / are shown
for holding the work in place. The number of these set-screws,

.50

JIG DESIGN

of course, depends entirely upon the size of the work and the
size of the holes to be drilled. Sometimes one set-screw is quite
sufficient, which, in this case, would be placed in the center, as
indicated by the dotted lines in Fig. 4.

The type of jig shown in Fig. 7 now possesses all the features

W' "."in

Fig. 6. Jig in Fig. 4 used in Combination with Two Parallels

generally required for a good jig, and presents a type which is
largely used in manufacturing plants, particularly for medium
and heavy work. The jig shown in Fig. 8, however, represents
another type, somewhat different from the jig in Fig. 7. The

Fig. 7. Jig improved by Adding Feet opposite Faces
containing Drill Bushings

jig in Fig. 7 is composed of two large separate pieces, which, for
large jigs, means two separate castings, involving some extra
expense in the pattern-shop and foundry. The reason for mak-
ing the jig in two parts, instead of casting it in one, is because it
makes it more convenient when machining the jig. The locat-

BOX JIGS

ing points, however, are somewhat hidden from view when the
piece is inserted. The jig shown in Fig. 8 consists of only one
casting L, provided with feet, and resembles an open drill jig.
The work is located in a manner similar to that already described,
and the leaf D, wide enough to take in all ,the bushings except
the one for the hole that must be drilled from the opposite side,
is fitted across the jig and given a good bearing between the
lugs in the jig wall. It swings around the pin E and is held down
by the eye-bolt F with a nut and washer. Sometimes a wing-
nut is handier than a hexagon nut. Care should be taken that

Fig. 8. Alternative Design of Jig in Fig. 7

the feet reach below the top of the nut and screw. The set-
screw G holds the work down, and takes the thrust when the
hole from the bottom side is drilled. The three holes A, A and
B are drilled from the top so that the thrust of the drilling of
these three holes will be taken by the bottom of the jig body L.
If one set-screw G is not sufficient for holding the work in place,
the leaf may be made wider so as to accommodate more binding
screws.

It is, however, an objectionable feature to place the clamping
screws in the bushing plate. If the leaf has not a perfect fit in
its seats and on the swiveling pin, the screws will tilt the leaf

JIG DESIGN

one way or another, and thus cause the bushings to stand at an
angle with the work, producing faulty results. In order to avoid
this objectionable feature, a further improvement on the jig,
indicated in Fig. 9, is proposed. In the jig body, the locating
points and the set-screws which hold the work against the locat-
ing pins are placed so that they will not interfere with two straps
Gy which are provided with elongated slots, and hold the work
securely in place, also sustaining the thrust from the cutting
tools. These straps should be heavily designed, in order to be
able to take the thrust of the multiple-spindle drill, because in
this case all the bushings, except the one for hole B, are placed

Fig. 9.

Jig in which Thrust of Drilling Operations
is taken by Clamps

in the bottom of the jig body. The leaf is made narrower and
is not as heavy as the one shown in Fig. 8, because it does not,
in this case, take any thrust when drilling, and simply serves the
purpose of holding the bushing for hole B. The leaves and loose
bushing plates for jigs of this kind are generally made of machine
steel, but for larger sized jigs they may be made of cast iron.
The leaf in Fig. 9 is simply held down by the thumb-screw H.

If the hole B comes near to one wall of the jig, it may not
be necessary to have a leaf, but the jig casting may be made with
a projecting lug D, as shown in Fig. 10, the jig otherwise being
of the same type as the one illustrated in Fig. 9. The projecting

BOX JIGS

part D, Fig. 10, is strengthened, when necessary, by a rib E, as
indicated. Care must be taken that there is sufficient clearance
for the piece to be inserted and removed. Once in a while it
happens, even with fairly good jig designers, that an otherwise
well-designed jig with good locating, clamping, and guiding
arrangements, is rendered useless, for the simple reason that there
is not enough clearance to allow the insertion of the work.

Fig. ii shows the same jig as before, but with the additional
feature of permitting a hole in the work to be drilled from the
end and side as indicated, the bushings E and F being added

Fig. 10. Modification of Jig Shown in Fig. 9

for this purpose. The bushings, in this case, extend through the
jig wall for some distance, in order to guide the drill closely to
the work. Bosses may also be cast on the jig body, as indicated
by the dotted lines, to give a longer bearing for the bushings.

Feet or lugs are cast and finished on the sides of the jig opposite
the bushings, so that the jig can be placed conveniently on the
drill-press table for drilling in any direction. When drilling
the holes from the bushings E and F, the thrust is taken by the
stationary locating pins. It is objectionable to use set-screws
to take the thrust, although in some cases it is necessary to do
so. When designing a jig of this type, care must be taken that
strapping arrangements and locating points are placed so that

JIG DESIGN

they, in no way, will interfere with the cutting tools or guiding
means. In this case the strap H is moved over to one side in
order to give room for the bushings F and the set-screw K.
Strap G should then be moved also, because moving the two
straps in opposite directions still gives them a balanced clamping
action on the work. If the strap G had been left in place, with
the strap H moved sideways, there would have been some ten-
dency to tilt the work.

Sometimes one hole in the work comes at an angle with the
faces of the work. In such a case the jig must be made along

1 ilk-p.^-^-4 ;t~~~

rrjrrir"""""" ir ~~]~

Fig. ii. Jig for Drilling Holes from Two Directions

the lines indicated in Fig. 12, the feet on the sides opposite to
where the drill bushings are placed being planed so that their
faces will be perpendicular to the axis through the hole A . This
will, in no way, interfere with the drilling of holes which are
perpendicular to the faces of the work, as these can be drilled
from the opposite side of the work, the jig then resting on the
feet B. Should it, however, be necessary to drill one hole at an
angle and other holes perpendicular to the face of the work
from the same side, an arrangement as shown in Fig. 13 would
be used. The jig here is made in the same manner as the jig
shown in Fig. 1 1 , with the difference that a bushing A is placed
at the required angle. It will be seen, however, that as the

BOX JIGS

other holes drilled from the same side must be drilled perpendicu-
larly to the faces of the work, it would not be of advantage to
plane the feet so that the hole A could be drilled in the manner
previously shown in Fig. 12. Therefore the feet are left to suit
the perpendicular holes, and the separate base bracket B} Fig.
13, is used to hold the jig in the desired inclined position when
the hole A is drilled.

Stand B in Fig. 13 is very suitable for this special work. It
is made up as light as possible, being cored at the center, so as
to remove superfluous metal. These stands are sometimes pro-

Fig. 12. Jig for Drilling Holes at an Angle

vided with a clamping device for holding the jig to the stand.
Special stands are not only used for drilling holes at angles with
the remaining holes to be drilled, but sometimes such stands
are made to suit the jig in cases where it would be inconvenient
to provide the jig with feet, finished bosses, or lugs, for resting
directly on the drill-press table.

When a jig of large dimensions is to be turned over, either for
the insertion or removal of the work, or for drilling holes from
opposite sides, it is, in cases where the use of a crane or hoist
can be obtained, very satisfactory to have a special device at-
tached to the jig for turning it over. Fig. 14 shows such an
arrangement. In this illustration, A represents the jig which is

JIG DESIGN

to be turned over. The two studs B are driven into the jig in
convenient places, as nearly as possible in line with a gravity axis.
These studs then rest in the yoke C, which is lifted by the crane
hook placed at D. The jig, when lifted off the table, can then
easily be swung around. The yoke is made simply of round
machine steel.

Fig- 13* Jig and Stand for Drilling Holes at an Angle

Fig. 14. Device for Turning over and Handling
Heavy Jigs

Examples of Closed or Box Jigs. — The development of a
closed or box jig has now been treated. In the following pages
a number of examples of closed jig designs will be shown and
described. There is, however, no distinct division line between
open and closed drill jigs, so that in many cases it is rather in-
consistent to attempt to make any such distinction.

BOX JIGS

In Fig. 15, for instance, is shown a box jig which looks like a
typical open jig. The jig body A is made in one solid piece,
cored out as shown in order to make it lighter. The piece to be
drilled, B, shown inserted in the jig, has all its holes drilled in
this jig, the holes being the screw holes C, the dowel pin holes D,
and the large bearing hole E. The bosses of the three screw holes
C are also faced on the top, and the bearing is faced on both sides
while the work is held in the jig. The work is located against
two dowel pins driven into the holes F, and against two lugs at
G, not visible in the illustration, located on either side of the

Fig. 15. Box Jig which Resembles the Open Type

work. In these lugs are placed set-screws or adjustable sliding
points. It may seem incorrect not to locate the bracket in
regard to the hole E for the bearing, so as to be sure to bring the
hole concentric with the outside of the boss. This ordinarily is
a good rule to follow, but in this particular case it is essential
that the screw holes be placed in a certain relation to the outline
of the bracket in order to permit this to match up with the pad
on the machine on which the bracket is used. Brackets of this
shape may be cast very uniformly, so that locating them in the
manner described will not seriously interfere with drilling the
hole E approximately in the center of its boss. The work is
firmly held in the jig by the three straps H, care being taken in
designing the jig that these straps are placed so they will not inter-
fere with the facing tools.

JIG DESIGN

The swinging strap /, which really is the only thing that makes
this jig a closed jig, serves the sole purpose of taking the thrust
of the heavy cutting tools when drilling the hole E and of steady-
ing the work when facing off the two ends of the hub. The two
collar-head screws K hold the strap to the jig body and the set-

Fig. 16. Plan and Elevation of Jig Shown in Fig. 15

screw L bears against the work. This strap is easily swung out
of the way by loosening one of the collar-head screws, a slot being
milled at one end of the strap to permit this. Stationary bush-
ings are used for the screw hole and dowel holes, but for the bear-
ing hole E three loose bushings and a lining bushing are employed.

BOX JIGS 59

The hole E is first opened up by a small twist drill, which makes
the work considerably easier for the so-called rose-bit drill. The
latter drill leaves TV inch of stock for the rose reamer to remove,
which produces a very smooth, straight, and concentric hole.
The last operation is the facing of the holes. The holes just
drilled are now used to guide the pilots of the facing tools, and,
as the operation is performed while the work is held in the jig,
it is important that the locating or strapping arrangements
should not be in the way.

In connection with the opening up of a hole with a smaller
drill, it may be mentioned that it is not only for large holes that
this method of procedure will save time, but the method is
often a time-saving one also for smaller holes, down to | inch in
diameter, when drilled in steel.

The use of lubrication in jigs is a very important item, the most
common lubricant being oil or vaseline, but soap solution is also
used. The objection to the latter is that unless the machine
and tools are carefully cleaned it is likely to cause rusting. Using
a lubricant freely will save the guiding arrangements, such as the
drill bushings, the pilots on counterbores, etc., to a great extent.

The jig in Fig. 15 is shown in Fig. 16 and a clear idea of the
design of the jig will be had by studying this line engraving.
The bracket B, in Fig. 15, could have been drilled in a different
way than described, which would sometimes be advantageous.
It could be held in a chuck, and the hole E reamed and faced in a
lathe, which would insure that the hole would be perfectly central
with the outside of the boss. Then a jig could be designed,
locating the work by a stud entering in hole E, as indicated in
Fig. 17, additional dowel pins and set-screws being used for
locating the piece sidewise. The whole arrangement could be
held down to the table by a strap and bolt, a jack-screw support-
ing it at the overhanging end.

Fig. 1 8 shows another jig of the closed type, with the work
inserted. The piece A is a casing, and the holes to be drilled
vary greatly in size. The casing rests on the flat, finished bottom
surface of the jig and is brought up squarely against a finished
pad at B. It further locates against the finished lug C, in order

JIG DESIGN

to insure getting the proper amount of metal around the hole D.
At the bottom it is located against the sliding point E, the latter
being adjustable, because the location of the work is determined
by the other locating points and surfaces. The work is held
against the locating points by the long set-screw shown to the
left. This clamping arrangement, however, is not to be recom-
mended, because this screw must be screwed back a considerable
distance in order to permit insertion and removal of the work.

,*^^ SCREW

jGjj

^^-•^""^

II ~\\

(,*-*""^

^^*

i i i

^^'

DRILL-PRESS TABLE

Fig. 17.

Simple Plate Jig for Drilling Bracket shown in Fig. 15,
after Hole £ has been Bored in the Lathe

An eye-bolt used in the manner described in a preceding chapter
would have given better service. The three straps G hold the
work against the bottom surface, and the two straps H hold it
against the finished surface at B. There is not a long finished
hole through the casting, as would be assumed from its appear-
ance, but simply a short bearing at each end, the remaining part
of the hole being cored out. For this reason, the hole is drilled
and reamed instead of being bored out, as the latter operation

BOX JIGS

would be a slower one. Although the two short bearings are
somewhat far apart, the guiding bushings come so close to these
bearings that the alignment can be made very good. The screw
holes and dowel pin holes at the bottom of the casing are not
shown in the illustration, as the inserted casing is not yet drilled.
The hole drilled from bushing / is a rather important hole, and
the bushing requires a long bearing in order to guide the drills
straight when drilling. When this jig was made, the projecting
lug which was provided solid with the jig body, to give a bearing

Fig. 18. Box Jig for Casing drilled from Five Directions

to the jig bushing, came so much out of the way in the rough
casting for the jig that half of the lining bushing would have been
exposed. It was therefore planed off and a bushing of the type
shown in Fig. 5, in the chapter on "Jig Bushings," inserted
instead, in order to provide for a long bearing.

Leaf K, which carries the bushings for drilling the hole D,
fits into a slot planed out in the jig body and is held down by
the eye-bolt L. Two lugs M are provided on the main casting
for holding the pin on which the leaf swivels. Around the hole

JIG DESIGN

D there are three small tap holes 0 which are drilled by the
guiding afforded by the bushing P, which is made of cast iron
and provided with small steel bushings placed inside as illustrated
in Fig. 14, in the chapter on " Jig Bushings. " In the bushing P
is another hole Q which fits over a pin located in the top of the
leaf and which insures that the three screw holes will come in
the right position. It should be noted that large portions of the

Fig. 19. Box Jig for Drilling Work shown by Dash-dotted Lines

jig body are cored out at top and bottom in order to make it
light and easy to handle. Of course some metal is also saved
by the construction of jigs in this manner, but comparing the
price of cast iron with the total price of a finished jig of this type,
the saving in this respect is so insignificant that it is not worth
while mentioning. The leaf K is also made of cast iron, being of

BOX JIGS 63

particularly large size, and it is planed at the places where it has
a bearing on the jig body.

Fig. 20 shows a closed jig about which there can be no doubt
but that it should be classified as a box jig. The piece of work
drilled, the foot trip A, has two holes B and C which are drilled
in this jig. The cylindrical hub of the work is located against
V-blocks and held in place by a swinging strap D. The work is
further located against a stop-pin placed opposite the set-screw
E. The trip is located sidewise by being brought against another

Fig. 20. Jig shown in Detail in Fig. 19

stop by the set-screw F. One-quarter of a turn of the collar-head
screw on the top of the jig releases the swinging strap which is
then turned out of the way; this permits the trip to be removed
and another to be inserted. Half a turn or less of the set-screws
is enough to release and clamp the work against the stops men-
tioned. A line engraving of this jig is shown in Fig. 19 which
gives a better idea of some of the details of the construction.

In Figs. 21 and 22 are shown two views of another type of
closed drill jig. The work A, to be drilled, is shown at the left

JIG DESIGN

in both illustrations, and consists of a special lathe apron with
large bearing holes, screw holes, and dowel pin holes to be drilled.
The apron is located in the jig body in the same manner as it is
located on the lathe carriage, in this case by a tongue which may
be seen at B in Fig. 22. This tongue fits into the slot C in the jig,

Fig. 21. Jig of Typical Design, and Work for which it is Used

Fig. 22. Another View of the Jig in Fig. 21

care being taken in the construction of the jig that the slot is
made deep enough to prevent the tongue from bearing in the
bottom of the slot. A good solid bearing should be provided,
however, for the finished surface on both sides of the tongue.
The surface D should also have a solid bearing on the surface E
in the jig, the difference in height between the two bearing sur-
faces in the jig being exactly the same as between the two bear-
ing surfaces on the lathe carriage where the lathe apron is to be
fitted. The work is brought up against, and further located by,

BOX JIGS 65

a dowel pin at the further end of the slot, by the set-screw in
the block F, Fig. 21. As it is rather difficult to get the tongues
on all the pieces exactly the correct width for a good fit in the
slot, the latter is sometimes planed a little wider and the tongue
is brought up against one side of the slot by set-screws. In
the case in hand, a few thousandths inch clearance is provided
in the slot, and the set-screw G in Fig. 22 is used for bringing the
work against the further edge, which stands in correct relation
to the holes to be drilled. The apron is held down against the
bottom surface of the jig by four heavy set-screws H.

It will be noticed that the jig is open right through the sides
in order to facilitate the finishing of the pads at the ends of the

Fig. 23. Jigs in which the Work is Located by Means of Beveled
Surfaces

work, and a swinging leaf, like the one previously described,
reaches across one side for holding the lining and loose bushings
for the hole K which is drilled and rose-reamed in the usual way.
The large hole V, Fig. 21, is bored out with a special boring tool
If, as there are no standard drills obtainable for this large size
of hole. This special boring tool is guided by a cast-iron bush-
ing which fits into the lining bushing; it is provided with two
cutters, one for roughing and one for finishing. The small
screw holes O around the large hole V are drilled from the bush-
ing P. For drilling the rest of the holes, except the hole Q,
stationary bushings are used. The screw holes ought to be
drilled simultaneously in a multiple-spindle drill. The jig is
provided with feet and cored out in convenient places in order

JIG DESIGN

to make it as light as possible to handle. Lugs project wherever
necessary to give ample bearings to the lining bushings and, in
turn, to the loose guiding bushings.

Fig. 23 shows two closed jigs made up of two main parts which
are planed and assembled by screws and dowels as indicated, the
reason for making the jigs in this way being the ease of planing
the bottom section. The work drilled in these jigs, some special
slides, is located by the dovetail and held up against one dove-
tail side by set-screws A} as shown in the illustration. In the jig

Fig. 24. Jig for Drilling Holes at other than go-degree Angles

to the left, the work is located endwise against a dowel pin and is
held up against this stop by a set-screw through the block shown
to the left. This block must be taken out when the slide is in-
serted, this being the reason why a lug cast directly in place,
through which the set-screw could pass, is not used. The top
plate D is held down on the main body by six fillister-head screws
Ej and two dowel pins F prevent it from shifting. No clamping
arrangements, except the set-screws A, are necessary. The
holes being drilled from the top, the main body of the jig takes
the thrust. These jigs are also used in multiple-spindle drills.

One objectionable feature of the jig to the right in Fig. 23 is
that set-screws A are difficult of access. There are, therefore,

BOX JIGS

holes piercing the heads of the set-screws in two directions in order
to allow a pin to be used when tightening the screws. A better
idea, however, is to have the screw-heads extend out through
the wall and, if this is solid, to have cored or drilled holes through
which the heads of the screws may pass.

In Fig. 24 is another closed drill jig in which the work is located
against the finished seats and held down by the set-screws A in
the straps B. All the holes, except those marked C, are drilled

Fig. 25. Jig in Fig. 24 in Position for Drilling Holes at an
Oblique Angle with Jig Base

in the usual manner, the jig standing on its own feet, but when
drilling the holes C, which come on an angle, the special stand
D is employed, which brings the holes in the right position for
drilling, as illustrated in Fig. 25. If only the holes C were to
be drilled, the feet on the side opposite the guiding bushings for
these holes could have been planed off, so that they would have
been in a plane perpendicular to the axis of the holes. This last
jig has a peculiar appearance, on account of the end walls coming
up square, as shown in the illustrations, but this design was
adopted only to simplify matters for the patternmaker, it being
easier to make the pattern this way.

CHAPTER IV
JIG BUSHINGS

The drills, counterbores, reamers, etc., used in connection
with drill jigs are guided by steel bushings, which are hardened
and ground, and placed in the jig body in their proper location.
These bushings may be of two kinds: stationary and removable,
the latter usually being known as ''loose" bushings. The most
common and the preferable form for the stationary bushing is
shown in Fig. i. This bushing is straight both on the inside
and on the outside, except that the upper corners A on the in-
side are given a liberal radius, so as to allow the drill to enter
the hole easily, while the corners B at the lower end of the out-
side are slightly rounded for the purpose of making it easier to
drive the bushing into the hole, when making the jig, and also
to prevent the sharp corner on the bushing from cutting the
metal in the hole into which the bushing is driven.

Removable Bushings. — When removable bushings are used,
they should never be placed directly in the jig body, except if
the jig be used only a few times, but the hole should always be
provided with a lining bushing. This lining bushing is always
made of the form shown in Fig. i. If the hole bored in the jig
body receives the loose or removable bushing directly, the in-
serting and removing of the bushing, if the jig is frequently
used, would soon wear the walls of the hole in the jig body, and
after a while the jig would have to be replaced, or at least the
hole would have to be bored out, and a new removable bushing
made to fit the larger-sized hole. In order to overcome this,
the hole in the jig body is bored out large enough to receive the
lining bushing referred to, which is driven in place. This lining
bushing then, in turn, receives the loose bushing, the outside
diameter of which closely fits the inside diameter of the lining
bushing, as shown in Fig. 2, in which A is the jig body, B the

BUSHINGS

lining bushing, and C the loose bushing. Both of these bush-
ings are hardened and ground so that they will stand constant
use and wear for some length of time. When no removable
bushings are required, the lining bushing itself becomes the
drill bushing or reamer bushing, and the inside diameter of the
lining bushing will then fit the cutting tool used. The bushing
shown in Fig. i is cheaper to make, and will work fully as well,
when driven in place in the hole receiving it, as do bushings
having a shoulder at the upper end, such as the loose bushing
shown in Fig. 2. It was the practice some years ago to make
all bushings with a shoulder, but this is unnecessary, and simply
increases the cost of making the bushing.

Material for Jig Bushings. — Bushings are generally made of
a good grade of tool steel to insure hardening at a fairly low
temperature and to lessen the danger of fire cracking. They

Fig. i.

Fig. 2.

Fig. 3-

can also be made from machine steel, which will answer all
practical purposes, provided the bushings are properly case-
hardened to a depth of about TV inch. Sometimes bushings for
guiding tools may be made of cast iron, but only when the cut-
ting tool is of such a design that no cutting edges come within
the bushing itself. For example, bushings used simply to sup-
port the smooth surface of a boring-bar or the shank of a reamer
might, in some instances, be made of cast iron, but hardened
steel bushings should always be used for guiding drills, reamers,
taps, etc., when the cutting edges come in direct contact with
the guiding surfaces. If the outside diameter of the bushing is
very large, as compared with the diameter of the cutting tool,
the cost of the bushing can sometimes be reduced by using an
outer cast-iron body and inserting a hardened tool steel bush-

yo JIG DESIGN

ing. Occasionally a bushing having a large outside diameter
is required as, for example, when a large counterbore must be
used in a small hole, which makes it necessary to have a large
opening in the jig body.

Dimensions of Stationary Jig Bushings. — Standard dimen-
sions for jig bushings, applicable under all circumstances, can-
not be given, as these depend, in most cases, on the different
conditions of the various classes of jigs in which the bushings
are inserted. The common practice is to make the length of
the bushing twice the inside diameter of the hole in the bushing
for stationary drill bushings. On very small bushings, however,
say J inch diameter hole and less, the length of the bushing will
have to be made longer than twice the diameter, while on very
large bushings the length may be made somewhat less than
twice the diameter. Table I gives proportions of stationary
drill bushings. The dimensions, as here given, will be found
suitable in all cases where no special conditions demand devia-
tion from ordinary practice. If the jig wall is thin, the bushing
may project out as shown in Fig. 3, so as to give the cutting tool
the proper guiding and support as close to the work as possible.
In Table II are given dimensions for lining bushings, not in-
tended to directly guide the drill, but to hold removable bush-
ings, which, in turn, guide the cutting tools. The dimensions
given in Tables I and II are for bushings made from either tool
steel or machine steel.

While it is difficult, in some cases, to draw a distinct line be-
tween stationary drill bushings and lining bushings, it may be
said, in general, that the bushings in Table I are used for guid-
ing the drills when drilling holes directly, either with a full-
sized drill, when the hole is not required to be very smooth or
accurate, or, if greater accuracy is required, for guiding a spot-
ting drill which fits the bushings exactly, after which the hole is
drilled out with a so-called " reamer-drill," which is o.oio inch
or less under the size of the finished hole, and finally reamed
out with a reamer exactly fitting the hole in the bushing. These
bushings are thus, in general, used when no tapping or counter-
boring would be required. The lining bushing in Table II,

BUSHINGS

again, may guide one of the tools for the holes to be finished
directly, and then removable bushings are inserted to guide the
other tools used.

Miscellaneous Types of Drill Bushings. — As mentioned, it
was, some years ago, general practice to provide even station-
ary bushings with a shoulder or head, as shown in bushing
C, Fig. 2. This will prevent the bushing from being pushed
through the jig by the cutting tool, but this seldom happens if
the bushings are made to fit the tool correctly. Sometimes the
shoulder is used to take the thrust of a stop-collar, which is

Table I. Dimensions of Stationary Drill Bushings

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IMe

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294

i'/4

1/6

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2/6

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i^i

iMe

I Me

2l/i

I 'He

2tt

27/6

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1 94

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1 96

1 94

29^

296

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396

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clamped on the drill, to allow it to go down to a certain depth,
as shown in Fig. 4, in which C is the stop-collar, D the wall of
the jig, and E the stationary bushing; F is the work. In such
a case, a shoulder on the bushing should be provided.

If the work to be drilled is located against a finished seat or
boss on the wall of the jig, and the wall is not thick enough to
take a bushing of standard length, then it is common practice
to make a bushing having a long head, as shown in Fig. 5.
The length A of the head can be extended as far as necessary
to get the proper bearing. As the bushing is driven in place

JIG DESIGN

and the shoulder of the head bears against the finished surface
of a boss on the jig, it will give the cutting tool almost as rigid
a bearing as if the jig metal surrounded the bushing all the way

up-
Removable bushings are frequently used for work which must

be drilled, reamed, and tapped, there then being one bushing
for each of the cutting tools. They are also used when different
parts of the same hole are to be drilled out to different diam-
eters, or when the upper portion of the hole is counterbored,

Table II. Dimensions of Lining Bushings

T""

Machinery, N.T.

l!-'2

1 1/2

2Me

21 He

2>4

I Me

I Hie

214

13/16

I7xi

2Me

2?4

25*

I Me

113,1s

JHe

JMe

I Me

liMe

2Me

3Me

iMe

2i/,

2i He

3Me

33/^

»*i«

i!4

HM«

2Me

33-^

I He

I Me

iJ4

I1 Me

2^6

or when a lug has to be faced o.L In this case, each tool, of
course, has its own guide bushing. The common design of
removable bushings is shown in Fig. 6. The outside is made
to fit the inside of the lining bushing with a nice sliding
fit, so that it can be gently pressed into the lining bushing by
the hand. The distance A under the head of the bushing
should be the same length as, or longer than, the guide bushing.
The thickness B of the head varies, of course, according to the
•size of the bushing. The diameter C of the head should be

BUSHINGS

from J to J inch larger than the diameter D of the bushing.
A groove E, f to J inch wide, is cut immediately under the
head, so that the emery wneel can pass clear over the part
being ground.

Means for Preventing Loose Bushings from Turning. — In
order to prevent the bushings from turning, in some shops a

Fig. 4-

Fig. 5-

Fig. 6.

collar, with a projecting tail, as shown in Fig. 7, is forced over
the head of the bushing. This arrangement also makes it easy
to remove the bushing. The dog, as it is commonly called, is
usually bent at the end of the tail, as shown in the illustration,
one end resting against some part of the jig, the proportions of
which the dog must suit. Sometimes the bent end is left straight,

Fig. 7.

Fig. 8. Fig. 9. Fig. 10.

if there is a possibility for the tail to strike against some lug in
the same plane. The making of such dogs involves some
extra expense, but it is very effective in avoiding troubles with
bushings turning and working their way out of the holes. In
some cases simply a hole is drilled in the shoulder of the bushing
at the edge, and a corresponding pin is driven into the jig body.
This serves the same purpose as the dog. It is probably cheaper,

TIG DESIGN

but it does not add the convenient means for removing the
bushing as does the dog. To make such a bushing more easily
removable, the arrangement shown in Fig. 8 is probably the
most common. A step A is turned down on the head, which,
in this case, will have to be a trifle larger in diameter. This
step permits some kind of a tool — a screw driver, for instance,
to be put underneath, and with a jerk the bushing may be
lifted enough to get a good hold on it. The half-round slot at B
is milled or filed in the periphery of the head, and fits over a pin
or screw which is fastened in the jig body, as mentioned before.

Machinery

Fig. n. Methods used for Preventing Jig Bushings from Turning

In Fig. ii are shown three methods of holding bushings to
prevent them from turning, the methods all being on the prin-
ciple described: A shows a bushing having a pin inserted which
slips in a slot cut in the lining bushing; B shows a bushing hav-
ing a slot milled through the collar, a pin being located in the
jig to engage this slot; and C illustrates a more elaborate device
that is sometimes used. The stop button which is fastened to
the jig prevents the bushing from being drawn out of the liner
while withdrawing drills or reamers, as well as preventing it
from turning.

The following method for holding slip jig bushings in place

BUSHINGS

has been found to be a very good one: Drill and tap a J- or
f-inch hole in the side of the jig bushing, as indicated in Fig. 12.
After the bushing is hardened and ground, screw in a pin and cut
it off so that it projects about T\ inch outside of the bushing, as
at B. Chip out a slot in each hole in the jig as indicated at A,
the hole being chipped in the direction of a spiral. By engaging
the projecting pin in this slot, the bushing is prevented from
turning and from rising out of the hole. At the same time it
can easily be removed when required, and there is no projection
on the jig of any kind that can be broken off while handling.
It is not always necessary to tap a hole for the pin in the jig
bushing. A plain drilled hole is sufficient when the bushing
is at least f inch thick. If the wall of the bushing is thinner
than this, the pin cannot be driven in tightly enough to stay in
place securely.

Machinery

Fig. 12. Another Method for Preventing Drill Bushings from Turning

Dimensions of Removable Bushings. — In Table III are given
dimensions for removable bushings of the type shown in Fig. 8.
Table IV gives dimensions for bushings for holes which are
reamed with a rose chucking reamer, after having first been
drilled with a drill TV inch smaller than the diameter of the
reamer with which the hole is finally reamed out. The bushing
to the extreme right, over the table, is the lining bushing, which
is made of machine steel, casehardened and ground. The
bushing to the extreme left is the bushing for the rose chucking
reamer. It is made of cast iron and ground. The bushing in
the center is the drill bushing which is made from tool steel,
hardened and ground, or, in cases where it does not seem war-
ranted to make the bushing of tool steel, of machine steel, case-
hardened and ground.

The tapered removable bushing shown in Fig. 9 is objection-

76 JIG DESIGN

Table III. Dimensions of Removable Drill Bushings

T*fl

•p

* *

. _~L

j±

"*1

3focA/nerj/,A[.r.

•

J-^2

]/^2

n/le

J-^2

JMe

l^i

iMe

1 1/4

I Me

iMe

IMe

I He

Z'Ma

I H

JMe

I V3

In/l6

i me

i?i

JMe

I Me

i?4

I me

l3^

zj$

!•}£

I He

I Me

zji

iMe

2j4

I JMe

I Me

2}<6

IiMe

2Me

I iMe

iMe

iiMfi

2Me

2He

i7-6

2i He

Me,

2He

I Me

I1 Me

2iMe

23/6

2Mo

•2^6

21/2

2Me

I Me

2Me

234

2^i

2Me

2]4

2Me

JiHe

2Me

?Me

33/^

2Me

I iMe

2Me

2lMe

Zjtj

254

33/4

3Vi

215/16

5^2

I iMe

21 He

33^

3Ji

215/16

5^2

23/4

3 Me

* When using dogs as illustrated in Pig. 7, the dimensions in these columns are omitted.

able on account of being expensive to make, and also on account
of being likely to be thrown out of true by chips, etc., forced in
between the outside of the bushing and the hole.

BUSHINGS

Screw Bushings. — Sometimes removable bushings are
threaded on the outside and made to fit a tapped hole in the
jig, as shown in Fig. 10. The lower part of the bushing is usu-
ally turned straight, and ground, in order to center the bushing
perfectly in the hole in the jig. The head of the bushing is
either knurled or milled hexagon for a wrench. When these
bushings are used, they are, as a rule, not used for the single
purpose of guiding the cutting tool, but they combine with this
the purposes of locating and clamping the work. For such

Table IV. Bushings for Holes Reamed with Rose Chucking Reamers

7f TT

it H

-± i. *

1^ * K ^1

ii=.

—

:-!<

F —

l<— I

I He
IH

I Me
iH
iMe

1 Me
I1 He
I 'Me

I1 Me
2

2 He
2^

2H
2%

I
I He

IMe

IMe
IMe

I Me
I 'He

I 'Me
2
2 He

2Me
2Me
2Me

2'H«

IMe
I Me

1 Me

I 'He
I 'Me
I 'Me
2

2 He

2Me
2%
2Me

2Me
2H
2i He

3
3H

i»H

I 'Me

I 'Me
2

2Me

2^
2Me
2*i
2i He
3

35/*6
3'Me

2H
2H
2%

23/4

3
3

4
4W

I Me

1 Me

2
21/6

2?6

2 ^

2%
2%
2%

3
3«

•Mr.

Me
He

Me
Me
Me
Me

W
Hi

Me
He

Me
Me

I M

I 'Me

2Me

2i He

3'He

4
4

I Me

I1 Me

2He
2H

3 Me

4W
4W
43/i
4W
4H

W
Mo
Me
Me
Me
Me
Me
Me
Me
Me
Me
Me
Me
Me

J/4
M
H

2H
2%
2H
2%
2H
2 'Me

3H
3H

3«

W
M

Me
Me
Me
Me
Me
Ha
Me
Me
Me
Me
Me
Me

JIG DESIGN

purposes they are quite frequently used. These bushings are
not commonly used as removable bushings, as it would take
considerable time to unscrew, and to again insert, a bushing of
this type into the jig body.

Special Designs of Guide Bushings. — When the guide bush-
ings are very long, and consequently would cause unnecessary
friction in their contact with the cutting tools, they may be
recessed, as shown in Fig. 13. The distance A of the hole in
the bushing is recessed enough wider than the diameter of the
tool so as not to bear on it. The length B, being about twice
the diameter of the hole, gives sufficiently long guiding sur-
faces for the cutting tool, to prevent its running out. If the
outside diameter of the bushing is very large compared with

Fig. 13. Fig. 14. Fig. 15.

the diameter of the cutting tool, as indicated in Fig. 14, the
expense of making the bushings may be reduced by making the
outside bushing of cast iron, inserting into this a hardened
tool-steel bushing, driven in place. The steel bushing is then
given dimensions according to Table I for stationary bushings.
The reason why there may be a necessity of a bushing having
so large an outside diameter and so small a hole may be that
the bushing is required to be removed for counterboring part
of the small hole being drilled by a counterbore of large diam-
eter, in which case the hole in the jig body has to be large enough
to accommodate the large counterbore.

If a loose or removable bushing is longer than the lining bush-
ing, as illustrated in Fig. 15, it will prove advantageous to have
the diameter of the projecting portion of the bushing about ¥V
inch smaller in diameter than the part of the loose bushing which

BUSHINGS

fits the lining bushing. This lessens the amount of surface
which has to be ground, and, at the same time, makes it easier
to insert the bushing, giving it, so to say, a point, which will
first enter the lining bushing, and it interferes in no way with
the proper qualities of the bushing as a guide for the cutting
tool.

In some cases, the holes in the piece to be drilled are so close
to one another that it is impossible to find space for lining
bushings in the jig. If this happens, it is necessary to make a
leaf, or a loose wall, or the whole jig, of machine steel or tool
steel, hardening a portion or the whole jig thus made.

Table V. Allowances for Grinding and Lapping Bushings

Operation

Diameter of Bushings in Inches

•

2\i

A
B

C
D

0.008
0.0005
0.008
0.0003

O.OIO

0.0005

O.OIO

0.0005

0.013
0.0007
0.013
0.0007

0.016
o . 0008
0.016
0.0008

0.020
0 . OOOQ
0.020

o . 0009

O.O25
O.OOI

0.025

O.OOI

A — Grind outside; B — Lap outside after grinding; C — Grind inside; D — Lap
inside after grinding.

Methods of Making Jig Bushings. — There are several methods
followed in turning jig bushings. Some toolmakers prefer to
" chuck out" the hole to the desired size and then finish the
outside of the bushing by placing it on an arbor; others prefer
to turn up the bushings two at a time, end to end, cut them
apart, and then bore as the final operation. This is an excellent
method to follow when making large bushings. The most rapid
method, however, is to chuck out the hole and finish the outside
at one setting, using bar stock held in the chuck of a rigid en-
gine lathe. This method is not always practicable on large
bushings.

In making allowances for grinding and lapping, many tool-
makers use too small limits, which is the cause of many bush-
ings having to be made over again on account of not " finishing
out." On the other hand, many toolmakers leave too liberal
an allowance for finishing, thereby causing unnecessary trouble

80 JIG DESIGN

and labor. The allowances given in Table V can be safely
used when the bushings are made somewhere near the propor-
tions indicated in Tables I to IV, but for extra long bushings
more liberal allowances should be made.

Before hardening, the bushings should be plainly stamped
with the size and purpose for which they are intended, "Jf
drill," "f ream," etc. They should be stamped with a set of
plain sharp figures, reserved solely for this purpose. It is poor
practice to try to stamp the words " drill," "ream," etc., in a
straight line, as this is difficult to do. If, however, the words
are laid out on a slight curve the results are more satisfactory,
as slight irregularities of alignment are not then so noticeable.
Sharp clean figures and letters, neatly laid out, not only improve
the appearance of the toolmaker's work, but also save the
drilling operator's time, as sharp clean-cut figures can be read
at a glance.

Hardening Jig Bushings. — When hardening bushings made
of tool steel they should be brought to an even red heat in a
clean fire; the heating should never be hurried. When bush-
ings are heated quickly, they are apt to heat unevenly, which
results in warping or distortion that makes it impossible to finish
them to the required size. Gas furnaces are excellent for heat-
ing, but a clean charcoal fire will answer the purpose. As soon
as the bushing has been brought to an even red heat, it should
be dipped in water just warm enough to take off the chill. The
bushing should then be heated to a "sizzling" heat, after which
it is left in the air to cool. Some toolmakers draw bushings to
a medium straw color. This is a mistake as it only tends to
shorten their life.

Grinding and Lapping. — There are four methods in common
use for finishing holes in jig bushings: i. Lapping with a lead
lap. 2. Lapping with a lead lap followed by a cast-iron or
copper lap. 3. Internal grinding. 4. Internal grinding fol-
lowed by a cast-iron or copper lap for removing the last 0.0005
inch. The first method is erroneous, as it invariably results in
bell-mouthed holes, especially when the toolmaker charges the
lap while in use, which is an unsatisfactory but very common

BUSHINGS

method. The second method is correct for holes too small to
be ground conveniently. The third method is inadvisable, as
the grinding wheel, no matter how fine, leaves innumerable
very fine scores and high spots. These high spots soon wear
away leaving the hole oversize. The last method is correct
and should be used whenever possible.

In Fig. 1 6 is shown a lead lap with a steel tapered spindle,
and a convenient mold for casting the laps. This mold is pro-
vided with a base having a
hole to receive the spindle
that the lap is cast on. A
number of laps can be cast
in this mold at one heating
of the metal, and the laps are
afterwards turned to the size
required. Fig. 17 represents
a familiar form of cast-iron
lap. This lap is split in three
places and provided with a
taper-end screw for expanding
it to compensate for wear.

Laps should be charged
before using — not while they
are in use. A good way
to charge a lap is to lay it
on a cast-iron plate on which
some of the abrasive mate-
rial has been sprinkled. A cast-iron plate small enough to be
conveniently handled is then held on the lap and moved back
and forth with a regular motion. The lap being rolled between
the two surfaces picks up a certain amount of the abrasive
material. A lead lap can be charged in this manner very
rapidly, as the grains of abrasive material readily imbed them-
selves in the soft metal. A cast-iron lap, being of a harder
material, requires more time to properly charge.

Until the last few years emery was the abrasive generally
used for lapping. At the present time, however, artificial abra-

Machinery

Fig. 1 6. Lead Lap and Mold used
for Casting it

82 JIG DESIGN

sives, products of the electric furnace, are displacing emery, as
they cut faster, producing excellent results in a comparatively
short time as compared to emery. Nos. 90 to 150 are used in
connection with lead laps for roughing operations. For the
final finishing with cast-iron laps, flour abrasive is used. When
not in use, any abrasive used for lapping should be kept in a
covered box to protect it from dirt and other foreign substances.
A small chip or piece of grit will often cut a deep score in a piece
of work.

Laps should always be run at a fairly low speed. Fifteen to
twenty feet surface speed for a lead lap used for roughing and

Machinery

Fig. 17. Usual Form of Cast-iron Lap

twenty to twenty-five feet surface speed for a cast-iron lap used
for finishing are about right. A high surface speed causes the
lap to wear out without cutting as rapidly as it should. Many
toolmakers make the mistake of running laps too fast, often
causing unsatisfactory work. For light lapping, the work can
be held by hand, but for a heavy roughing cut it is best to hold
the work with an ordinary lathe dog, care being taken to see
that the dog is not clamped so tightly as to spring the work
out of shape. Lead laps should be split to compensate for wear,
and the spindles should have a groove cut along their entire
length to prevent the lap from turning.

Before testing with a size plug, the work should be washed
with benzine or gasoline to remove all traces of the abrasive
material, a few grains of which will wear the size plug below
standard size in a surprisingly short time.

Many toolmakers look on the finishing of jig bushings by
internal grinding as a rather uncertain method, whereas it is a
comparatively simple process when the following important
factors are carefully considered. First, proper selection of grind-
ing wheels; second, correct wheel speeds or at least as nearly

BUSHINGS 83

correct as the design of the machine will permit; third, correct
alignment of the headstock in regard to the travel of the platen;
and fourth, proper truing of wheels.

Wheels for internal grinding should be of a medium grit,
soft grade and open bond. As a rule the grit should never be
finer than 60 grit; in fact, a coarser grit can often be used to
advantage. Wheels with fine grit cut slowly, and fill up readily,
glazing and invariably heating the work, and causing chattering
and other troubles. In fact, the only argument in favor of a
fine grit wheel is that it leaves a smooth surface. However, no
matter how smooth the surface appears, even under a powerful
glass, it must be lapped to remove the wheel marks.

For the internal grinding of jig bushings, aloxite wheels, if
inch in diameter, f -inch face, 60 grit, P grade, 0-495 bond, may
be used with good results, the wheel speed being 12,000 R.P.M.
For bushings averaging 2\ inches long, if -inch hole, the holes
rough-bored, 0.015 inch being left for grinding, the grinding
time per bushing, including chucking and truing up, would be
about twelve minutes each, and the finish left good, 0.0005
inch being sufficient to lap out the wheel marks. Reference is
made to the holes being rough-bored; this is good practice, as
the rather rough surface tends to wear the wheel just a little
while removing the fire scale, thus preventing the wheel from
glazing. Once the scale is removed from the hole, the wheel
should not glaze readily, provided it is of the proper grit and
grade.

Wheels for internal grinding should be run at a surface speed
of 5000 feet per minute. This, however, is a general rule open
to exceptions. A safe practical rule to follow is to speed up the
wheel if it wears away too readily, and to reduce the speed where
the wheel shows a tendency to glaze. Attention to this rule
will often save much trouble. The toolmaker should bear in
mind the fact that it is easier to adjust the speed to suit the wheel
than it is to try to keep on hand a large variety of wheels to suit
all speed conditions.

Assuming that the work in question is to be done on an ordi-
nary universal grinder, the headstock must be set parallel with

84 JIG DESIGN

the travel of the platen to produce straight holes. A practical
way to determine parallelism is to clamp a piece of round
stock in the headstock chuck, letting it project from the jaws a
little farther than the length of the holes to be ground. This
piece should have a groove turned in it for the wheel to dwell
in during reversal. This test piece is then ground in the regular
way with the wheel used for cylindrical work, the headstock
being adjusted by means of its swivel base until the test piece
is ground parallel. Before calipering, the wheel should be al-
lowed to grind until very few sparks are visible. When once
this test piece has been ground straight the setting can be de-
pended upon to produce straight holes, provided, of course,
that the swivel adjustment of the headstock and the angular
adjustment of the platen are not disturbed. To try to align
the headstock by calipering the work while the internal grinding
is in process is, at best, difficult, and the operator is never sure
of accurate results.

It is common practice to true wheels for internal grinding
with a diamond fed by hand, using the eye as a guide. This
is poor practice, as the wheel is seldom turned parallel, one
edge being left to do all the cutting, which glazes it readily. A
more practical way to true these comparatively soft wheels is
to feed them past the end of a carborundum rub, in 20 grit, H
grade. The rub can be held in a suitable holder strapped to
the platen of the grinder or held firmly by hand against the end
of the work. A carborundum rub shows high efficiency when
used for this purpose.

In holding work in the chuck for internal grinding, it is well to
exercise due care to see that the work is not clamped hard
enough to spring it out of shape. As a rule it does not require
much pressure to hold work of this nature, as the grinding cut
is comparatively light. As it is general practice to grind internal
work dry, a certain amount of expansion from frictional heat is
always present. For this reason considerable care has to be
used in calipering the work with the sizing plug. As the plug is
many degrees cooler than the work, it is liable, on being inserted,
to contract the bushing suddenly, causing bushing and plug to

BUSHINGS 85

"freeze" together firmly. This can be avoided by cooling the
work with a plug that is known to be undersize before caliper-
ing with a plug of the desired size.

When a wheel of 60 grit is used, a hole one inch or under in
diameter should be left approximately 0.0005 mcn undersize.
This amount is sufficient to lap out the wheel marks and leave
a "dead smooth" mirror finish to the hole. This is a general
rule based on the fact that a certain amount (in this case 0.00025
inch) is enough allowance to lap out the marks left on a surface
by a grinding wheel, and that should suffice for all holes regard-
less of size. With comparatively large holes, one and one-half
inch diameter or over, it is better, however, to make allowance
for finishing, owing to the fact that the area of contact of wheel

ftZ^^^^

l^^^^

Machinery

Fig. 18. Arbor for Holding Bushings

and work is generally not so great and the ground surface is not
quite so smooth.

In regard to the external grinding of bushings, there are two
important points that should be given consideration: the selec-
tion of wheels and the method of holding the work. The
wheel should be fast cutting and at the same time it should hold
its shape and leave a good finish. For this work good results
may be obtained with an aloxite wheel of 1 2 inches diameter, |-
inch face, 5-inch hole, 405 grit, N grade, D-497 bond, the wheel
being run at a speed of 1800 R.P.M.

When a number of bushings arc to be ground one after another
it is best to mount them on arbors of the same length, when
practicable to do so, thus saving considerable time generally
spent in re-setting the platen, which has to be done whenever
the tailstock is moved to accommodate arbors of different
lengths. An arbor for holding bushings should be made as
shown in Fig. 18. The straight part should be a good fit in the

86 JIG DESIGN

bushing, a slight taper on the remainder of the arbor being
sufficient to prevent the bushing from turning on the arbor.
When bushings are held on an ordinary arbor or mandrel the
operator is never quite sure that the hole and the outside of the
bushing are concentric, as one end of the arbor, owing to its
taper, does not quite fill the hole. This is illustrated in Fig. 19.
Both Figs. 1 8 and 19 are somewhat exaggerated to illustrate
the principle.

In grinding lining and solid bushings, due allowance must be
made for a driving fit in the body of the jig. There are three
methods in common use for making driving fits on this class of
work: First, grinding the bushing until the lower end just
enters the hole, the bushing being slightly tapered to bring it
to a snug fit when pressed into place; second, grinding the

v//////////////////^^^

\ \

V//////////////////^^^

Fig. 19. Improper Fit of Bushing on Ordinary Arbor

bushing straight for its entire length, leaving it just enough
oversize to make a good driving fit; and third, grinding the
bushing for nearly its entire length just enough oversize to
make a good driving fit, and grinding about one-eighth its length
just enough undersize to enter the hole.

The first method is not considered very good practice, as the
bushing contracts more at the top than elsewhere, owing to the
taper, which leaves the hole in the bushing tapered. The sec-
ond method is very poor practice, as the bushing is liable to
cramp while being forced in place, which results in an unsatis-
factory job, as the hole in the jig is generally sheared by the
sharp end of the bushing. The third method is correct, as the
part that is ground to fit the hole acts as a pilot, thus insuring
the proper starting of the bushing, and the body, being straight,
insures even contraction.

In making allowances for driving fits, o.ooi inch for each

BUSHINGS

inch diameter of the bushing is considered practical where the
holes are one inch or over, and where the holes in the jig are
bored smooth. If the holes are rough-bored, a more liberal
allowance is required. After the lining bushings are driven in
place, they require re-lapping, as they always contract a little.

The outside of the removable bushings should be finished
by lapping to a "dead smooth" finish, as otherwise they will
soon wear loose. This should never, under any circumstances,
be done with emery cloth, but with a cast-iron lap as illustrated
in Fig. 20. The abrasive used in this case should be of flour
grit with lard oil as a lubricant, the abrasive and oil being
applied through a hole in the top of the lap. The work should
be lapped with a regular even motion to insure its being

Machinery

Fig. 20. Lap for Finishing Outside of Slip Bushings

straight, and should be brought to the temperature of the room
by being cooled in benzine or gasoline before testing for a fit.
The lapping should be carried to a point where the bushing is
a wringing fit in its liner, but not tight enough to stick when
left for a moment.

After the grinding and lapping of the removable bushings,
their tops can be finished by lapping on a carborundum stone,
in medium grit, wet with gasoline. A regular motion should
be used across the face of the stone without turning or altering
the relative position of the bushing. This lapping gives the
bushings a good appearance, and, as the dimensions stamped
are left black from the action of the fire in hardening, they
can be read at a glance.

Driving Fit Allowances for Jig Bushings. — Standard dimen-
sions for driving fit allowances for jig bushings, arranged ac-
cording to the outside diameter of the bushing, are given in

JIG DESIGN

Table VI. Oftentimes difficulty is experienced in assembling
the bushings on account of not having allowed the proper
amount of stock for fitting.

Plate Bushing Holders for Multiple Drilling. — When a
number of holes are to be drilled and reamed on a multiple-
spindle machine, the most simple method is to place the piece
in a suitable jig and use individual slip bushings, so that after
the holes are drilled the bushings can be replaced with reamer-
Table VI. Allowances for Driving Fit for Drill Bushings

Outside
Diameter,
Inches

Allowance
for
Drive Fit,
Inch

Outside
Diameter,
Inches

Allowance
for
Drive Fit,
Inch

Outside
Diameter,
Inches

Allowance
for
Drive Fit,
Inch

3A6

O.OOI

7/8

0.0015

i 5/8

0.0025

S/i6

O.OOI

0.0015

13/4

0.0025

7/16

O.OOI

1/16

O.002

i 15/16

0.0025

1/2

O.OO-I

1/8

O.OO2

2 1/8

0.003

9/i6

O.OOI5

O.OO2

21/4

0.003

11/16

0.0015

5/i6

O.O02

2 7/16

0.003

3/4

0.0015

3/8

O.OO2

25/8

0.0035

13/16

0.0015

7/16

0.002

2 3/4

0.0035

size bushings, the jig moved under the reamers, and the holes
machined. The loss of time in handling these slip bushings
is so great that the production costs increase very rapidly,
especially when the operator has to stop to pry up bushings
with a screwdriver or some other tool, as is often the case.
This style of bushing will frequently catch the drilling or ream-
ing tool and turn with it, thus wearing the bushing plate. To
prevent its turning, the groove-cut bushing is sometimes used.
This consists of an ordinary slip bushing in which a slot is cut
spirally around one-quarter of the outer periphery. This slot
engages a pin in the bushing plate, so that, when the bushing
starts to slip, the pin prevents its making a full turn. A modi-
fication of this method was described in connection with Fig. 12.
One source of trouble from individual slip bushings is the
accumulation of chips, which must be carefully removed before
the bushings are changed; another is the possibility of inter-

BUSHINGS

changing the drilling and the reaming bushings (even though
they are carefully marked) and thus spoiling the tools or the
work. An improvement over the individual slip bushings is

\ '•' /' / TO FIT

BUSHING
BORE
IN JIG

rTh

] L

«_ DIAMETER BUSHINQ
BORE IN JIG

Marlilnrry

Fig. 21. Drill with Guide
Bushing attached

Fig. 22. Stationary Guide for Multiple
Drilling and Reaming Tools

the plate bushing holder, which is especially useful on such
work as crankcases, cylinders, etc., and in practically all work
where six or more holes are to be drilled. The work is placed
in a box jig or frame in which there are either two dowel-pins

90 JIG DESIGN

or two slots. The removable bushing plates used with this
frame have holes or hinged binders to correspond with these
pins or slots and so are correctly located.

Guide Bushings attached to Drills. — When several small
holes necessitating two or more operations are to be machined,
the following plan works well from a production standpoint.
Guide bushings of the same diameter are fastened to the drills,
reamers and other tools to locate them in the bushings in the
plate, which are uniform in diameter. Thus, when drilling or
reaming, the tools will be guided from the bushing A, Fig. 21.
This method is not recommended for holes over one inch deep,
as there is a tendency for the drills to spring out of alignment,
especially if the drilling is done against a rough surface, since
the end of the drilling tool will be some distance from the aux-
iliary bushing guiding it. This arrangement is effective for
drilling steel, as the space between the jig plate and the work
allows room for the curled chips. The diameter of the guide
bushing, however, must be kept as small as possible, since this
piece has a tendency to heat and stick owing to the peripheral
speed. This sticking and the wear on the bushing plate may
be avoided by using a stationary pilot similar to that shown in
Fig. 22. A Z-shaped casting with a bore equal to the tool size
and a nose equal to the jig bushing diameter is secured to the
arm of the multiple-spindle drilling machine by a bolt that
extends through the slot in the arm, as shown in the illustration.

General Notes on Bushings. — When accurate work is neces-
sary, the bushings should support the cutting tool to within
one diameter of the tool from the work. If a A-inch drill is
used, the end of the bushing should not be more than -fe inch
from the work, and it may be carried to within J inch of the work.
Bushings should not be located close to the work with the object
of carrying the chips up through the bushing. It is much better
to provide other means in the jig for the removal of the chips.

The shape of the work frequently requires bushings of con-
siderable length in order to carry the cutting tool close to the
work. When the length exceeds four diameters of the tool to
be guided, the bushing presents considerable friction surface.

BUSHINGS gi

A length equal to two diameters of the cutting tool is usually
sufficient for a bearing surface in the bushing. The remainder
of the length of the hole in the bushing may be counterbored
or relieved. The end that should be relieved is, of course, that
which is farthest from the work into which the tool is to be
guided.

Screw bushings are generally avoided when accurate work is
required. There must be a certain amount of clearance in the
ordinary tapped hole, and a threaded bushing is likely to be
out of true on that account. Sometimes, however, it happens
that no other type of bushing can be used for the work in hand.

The headed or flanged bushing is preferred by many tool
designers as a lining bushing, whenever it is possible to utilize
it. If it is desired to have the head of the bushing flush with
the surface of the jig, the jig is counterbored to receive the head.

As previously mentioned, slip bushings are employed when
several operations are to be performed through the same lining
bushing. For example, when it is desired to drill and ream a
hole and to finish a boss or spot around the hole while the work
is still in the jig, a lining bushing is selected that will guide a
counterbore iV inch larger than the boss to be finished. A slip
bushing is then made to guide the drill, the body of which is
a sliding fit in the lining bushing. Another slip bushing is made
for the reamer which is also a sliding fit in the lining bushing.
The slip bushing walls may have any thickness, providing they
are not too thin. Should the conditions require bushings with
too thin walls, the counterboring operation in the jig must
be abandoned and some different method of procedure adopted.

CHAPTER V
LOCATING POINTS AND ADJUSTABLE STOPS

The locating points in a jig usually consist of finished pads,
bosses, seats, or lugs, cast solid with the jig, as illustrated in
Fig. i . In this engraving the surfaces marked / are the locat-
ing points, which bring the piece to be machined in correct re-
lation to the bushings guiding the drills, or to the gages to which
other cutting tools may be set. This method of locating the
work is satisfactory when the work done is finished in a uniform
way and where there is very little variation in the parts inserted
in the jig.

Pins and Studs used as Locating Means. — Another com-
monly used method for locating the work in jigs is by means of
dowel pins, as shown at A and B in Fig. 2. The sides of the
dowel pins which rest against the work are usually flattened,
as indicated, so as to give more bearing than a mere line con-
tact with the pins could give, and, at the same time, prevent
too rapid wear on the locating pins, as would be the case if the
work bear against the pins along a line only.

Sometimes pins or studs are inserted in jigs to act as locating
points, instead of having lugs cast directly on the jig as shown
in Fig. i. A case where a pin is used for this purpose is shown
in Fig. 3, where B is the body of the jig, A the pin inserted to
act as a locating and resting point, and C the work located
against this point. Locating pins of this character should
always be provided with a shoulder or collar, so that they will
firmly resist the pressure of the work they support, without
possibility of moving in the hole in which they are inserted.

Locating by Means of V-blocks. — A common method of
locating cylindrical pieces or surfaces is that of placing the
cylindrical surface in a V-block, as shown in Fig. 4. This
V-block, as a rule, is stationary, and is held in place by screws

LOCATING POINTS

and dowel pins, as indicated in the engraving, but sometimes
this V-block may also be made adjustable, in order to take
up the variations of the pieces placed in it, and also in order
to act as a clamp. A V-block of this character is shown in
Fig. 5. In this, A is the adjustable V-block, having an oblong

\-fJ

Fig. i. Locating Pads
in Jigs

Fig. 2. Pins used for
Locating Work

hole B to allow for the adjustment. The block is held down
in place by a collar-head screw C, which passes through the
elongated hole. The under side of the block is provided with a
tongue Z), which enters into a slot in the jig body itself, the
V-block being thereby prevented from turning sideways. The

Fig. 3. Inserted Pin used
for Locating and Support-
ing Work

Fig. 4. V-block for Locating
Round Work or Cylindrical
Surfaces

screw E passes through the wall of the jig, or through some
lug, and prevents the V-block from sliding back when the work
is inserted into the jig. It is also used for adjusting the V-block
and, in some cases, for clamping the work. The V-blocks are
usually made of machine steel, but when larger sizes are needed
they may be made of cast iron. Little is gained, however,

JIG DESIGN

in making these blocks of cast iron, as most of the surfaces
have to be machined, and the difference in the cost of material
on such a comparatively small piece is very slight.

Cup and Cone Locating Points. — When it is essential that a
cylindrical part of the work be located centrally either with the
outside of a cylindrical surface or with the center of a hole

Fig. 5. Adjustable V-block used for Locating Purposes

passing through the work, good locating means are provided
by the designs shown in Figs. 6 and 7. In Fig. 6, the stud A
is countersunk conically to receive the work. The stud A is
made of machine or tool steel, and may, in many cases, serve
as a bushing for guiding the tool. In Fig. 7, the stud is turned
conically in order to enter into a hole in the work. These two

WORK

Fig. 6. Recessed Stud used Fig. 7. Conical Stud used
for Locating Round Work for Locating Work in Re-
in a Jig with Relation to lation to the Center of
the Center a Hole

locating appliances are always made stationary, and are only
used for locating the work, never for binding or clamping.

Screw Bushings and Sliding Bushings used as Locating
Means. — Screw bushings may be used for locating and clamp-
ing purposes by making them long enough to project through
the walls of the jig and by turning a conical point on them, as

LOCATING POINTS

shown in Fig. 8, or by countersinking them, as shown in Fig. 9.
In all cases where long guide bushings are used, the hole in the
bushing ought to be counterbored or recessed for a certain dis-
tance of its length.

Another type of bushing which serves the same purpose as a
screw bushing is illustrated in Fig. 10. This bushing, together
with the forked lever D and clamping bolt and wing-nut shown,
will serve not only to locate but also to clamp the work in place.
This sliding bushing gives very good results and is preferable
to the screw bushing in cases where accurate work is required;
but, as a rule, where extreme accuracy would be required, this
kind of locating means is not used.

In Fig. 10 the sliding bushing A has a close sliding fit in the
lining bushing B. In the head of the bushing A there are two

Figs. 8 and 9. Screw Bushings

screws with hardened heads, which fit into elongated slots in
the forked lever or yoke D, which, in turn, swivels around pin
E. The eye-bolt F fits into a slot G in the yoke, and the wing-
nut tightens down the bushing against the work as clearly indi-
cated in the engraving. A comparatively long bearing for the
bushing is required in order to produce good results. On work
that varies considerably in size, this arrangement works some-
what quicker than does a screw bushing, but it is clearly evident
that it is a rather expensive appliance and that the construction
of the jig does not always permit of its application.

In some instances it is necessary to have the screw bushing
movable sideways, for instance, when the piece of work to be
made is located by some finished surfaces, and a cylindrical
part is to be provided with a hole drilled exactly in the center

JIG DESIGN

of a lug or projection, the relation of this hole to the finished
surfaces used for locating being immaterial. The piece of work,
being a casting, would naturally be liable to variations between
the finished surfaces and the center of the lug, particularly if
there are other surfaces and lugs to which the already finished
surfaces must correspond, and in such a case, the fixed bushing
for drilling a hole that ought to come in the center of the lug,
might not always suit the casting. In such a case, so-called
" floating" bushings, as shown in Fig. n, are used. The screw

WORK

Fig. 10. Sliding Bushing for Locating and Clamping Work

bushing A is conically recessed and locates from the projection
on the casting. It is fitted into another cylindrical piece B,
provided with a flange on one side. The piece B, again, sets
into the hole C in the jig body Z), this hole being large enough
to permit the necessary adjustment of the jig bushing.

When the bushing has been located concentric with the lug
E on the work, the nut F, having a washer G under it, is tightened.
The flange on piece B and the washer G must be large enough
to cover the hole C even if B is brought over against the side

LOCATING POINTS

of the hole. It is not often necessary, however, to use this
floating bushing, because it is seldom that a drilled hole in a
piece of work can be put in without having any direct relation
to other holes or surfaces.

Adjustable Locating Points. — The most common form of ad-
justable locating points is the set-screw provided with a check-

Fig, ii. Floating Drill Bushing

Fig. 12. Adjustable Locat-
ing Point

nut, as shown in Fig. 12. The screw A is a standard square-
head set-screw, or, in some cases, a headless screw — with a
slot for a screw driver; this screw passes through a lug on the
jig, or the jig wall itself, and is held stationary by a check-nut C

Fig. 13. Adjustable Locating Point consisting of a Flatted
Stud held in Place by a Set-screw

tightened up against the wall of the jig. Either end of this
screw may be used as a locating point, and the check-nut may
be placed on either side. By using a square-head screw, adjust-
ment is very easily accomplished, but unless the operator is
familiar with the intentions of the designer of the jig, locating

JIG DESIGN

points of this kind are often mistaken for binding or clamping
devices, and the set-screws are tightened up and loosened to
hold and release the work, when the intention is that these
screws should be fixed when once adjusted. It is not even
possible to depend upon the check-nut stopping the operator
from using the screw as a binding screw. A headless screw,
therefore, is preferable, as it is less apt to be tampered with.

The sliding point, as illustrated in Figs. 13 and 14, is another
adjustable locating point which is used to a great extent in jig
work. A flat piece of work or a plate which is not perfectly
level will always rock if put down on four stationary locating

Fig. 14. Sliding Point used for Locating Work

points, but the difficulty thus encountered is very easily over-
come by making one of the locating points adjustable, and, as a
rule, the sliding point is used for this purpose.

One design is shown in Fig. 13, where A represents the work
to be located, B the sliding point itself, and C the set-screw,
binding it in place when adjusted. The sliding point B fits a
hole in the jig wall and is provided with a milled flat slightly
tapered, as shown, to prevent its sliding back under the pressure
of the work or the tool operating upon the work. This design
of sliding point is frequently used, but it is not as efficient as
the one illustrated in Fig. 14. In this design the sliding point
A consists of a split cylindrical piece, with a hole drilled through
it, as illustrated in the engraving, and a wedge or shoe B tapered
on the end to fit the sides of the groove or split in the sliding
point itself. This wedge B is forced in by a set-screw C, for the

LOCATING POINTS

purpose of binding the sliding point in place. Evidently, when
the screw and wedge are forced in, the sliding point is expanded,
and the friction against the jig wall D is so great that it can
withstand a very heavy pressure without moving. Pin E pre-
vents the sliding point from slipping through the hole and into
the jig, when loosened, and also makes it more convenient to
get hold of. In the accompanying table are given the dimen-
sions most commonly used for sliding points and binding shoes
and wedges.

Special Types of Adjustable Stops. — Adjustable stops are
used to a greater extent in milling fixtures than in drill jigs, but

Dimensions of Sliding Points and Shoes or Binders

Screws Me

H
21A to 3

2J4 to 3
H

2J4 to 3

5A6

U
2}4 to 3

M
M

9*2

the principles employed are the same. The examples shown in
connection with the following description of adjustable stops
have been applied to milling fixtures, and, in some cases, to drill
jigs. In Fig. 15 is shown the simplest type of adjustable stop,
provided with a helical spring beneath the plunger, to press it
against the work. The objection to this type of stop is that
the plunger A will slip back under the pressure of the clamps or
cutting tools upon the work. There is also danger of the milled
flat on the plunger clogging with dirt, so that the stop will not
work properly. Considerable time is, therefore, lost in using
jigs or fixtures with this type of stop. The method of clamping
the plunger is also slow, as it is necessary to use a wrench in
tightening or loosening the set-screw B. In Fig. 16 is shown an
adjustable stop which is an improvement over that shown in
Fig. 15. The flat on the side of plunger A is milled at a slight

100

JIG DESIGN

angle instead of parallel with the center-line, as in Fig. 15.
This prevents the plunger from slipping after being clamped.
A piece of hardened drill rod B, which is kept from turning by a
small pin C, engaging a flat milled in piece B, is used between
the plunger A and the clamp. A wing-nut D is fastened to the

| WORK

Machinery

Fig. 15. Simple Type of
Adjustable Stop

Fig. 1 6. Improvement on Stop
shown in Fig. 15

end of the screw as shown, in order to eliminate the use of a
wrench.

In Fig. 17 is shown another adjustable stop which presents a
further improvement over that shown in Fig. 16. A bronze
bushing B is driven into the base of the jig and allowed to pro-

Machinery

Fig. 17. A Further Improvement upon the Adjustable Stops
shown in Figs. 15 and 16

ject above the base, as indicated. Plunger A is a sliding fit in
the bushing. A cap C is driven onto the end of the plunger
and extends down over the outside of the bushing, as indicated,
making the stop dirt-proof. This stop, however, as well as that
shown in Fig. 16, is not entirely satisfactory, because it will

LOCATING POINTS

101

shift at the time it is tightened, although when once tightened
it will remain in position.

In Fig. 1 8 a different arrangement is shown. Here the
thumb-screw and spring plunger used in the preceding device
is abandoned, and the sliding wedge A is used to obtain the
pressure upon plunger C. The wedge is provided with a handle
B attached so that it can easily be operated, and is held in place
by two shoulder screws that are inserted through two elongated
slots milled in the wedge. These screws are tightened after the
stop has been brought up to position. The difficulty met with
in using this stop is that the wedge is liable to slip back, owing to

Machinery

Fig. 1 8. Simple Form of Adjustable Wedge Stop

the vibration of the machine while in operation, so that plunger
C drops down.

In Fig. 19 is shown a further development of the method
indicated in Fig. 18. In this case, means are provided for pre-
venting wedge A from slipping back. A stud is riveted into
the wedge A, this stud extending up through an elongated slot
cut in the base of the fixture. The end of the stud is threaded
for the knurled nut B, which also acts as a handle for shifting
the wedge. When this nut is tightened, it clamps the wedge A
and the shoe C against the base. The friction between shoe C
and the base prevents the slipping of wedge A. Shoe C also
acts as a covering for the slot cut in the base, and thus acts as
a dirt and chip shield. It is prevented from turning, when the
nut B is tightened or loosened, by a stud D, driven into it and
sliding in a slot cut in the base. The difficulty with this design
is that wedge A rests upon the table of the machine, and, if there
is slight unevenness in the table, the plunger is liable to spring
down slightly under the pressure of the cut.

102

JIG DESIGN

In order to overcome this difficulty, an adjustable stop, as
shown in Fig. 20, has been designed. The flat style of wedge is
abandoned, and the wedge A is made of drill rod and slides in
a hole drilled in the base of the fixture. The stud at the back
end of the wedge is screwed into it instead of being riveted, as
in the previous example. Bushing C is provided with a shoulder
and a headless set-screw D is added to prevent plunger E from
dropping out when the fixture is not in use. The wedge A is
subjected to considerable friction and the fixture is, therefore,
not so sensitive to the touch of the operator as would be desir-

x Machinery

Fig. 19. Improvement upon the Adjustable Wedge Stop
shown in Fig. 18

able. It is difficult for the operator to feel when the stop is
against the work, when tightening the wedge in position.

Fig. 21 shows a modification of the design shown in Fig. 20,
the only change made being in bushing A, which has been
lengthened so that it will act as a support for the end of wedge B.
The bushing is made of cold-rolled steel and casehardened.
The bottom part of the base is cut away in order to reduce the
friction between the base and the wedge. This design is better
than that shown in Fig. 20.

In Fig. 22 is shown a somewhat complicated and expensive
adjustable stop which, however, has the advantages of almost
perfect operating conditions. Bushing A is lengthened and has

LOCATING POINTS

I03

a much larger shoulder in order to take the thrust to which it
will be subjected when the device is operated. A small pin B
replaces the headless set-screw used in the designs in Figs. 20
and 21. The arrangements for clamping the wedge have been
considerably changed, and bronze casting C is added. A hole
is cut in the base into which the casting is inserted, clearance

Machinery

Fig. 20.

A Further Improvement upon the Adjustable Wedge
Stops shown in Figs. 18 and 19

being permitted all around so that the casting can be aligned
easily with the wedge. The casting is held in place by two
fillister-head screws and two dowels; a hole is drilled through
the lower part of it which acts as a support for the back end of
the wedge, as indicated. The front end is supported in the
bushing A in such a manner that the friction is reduced to a

Machinery

Fig. 21.

A more Satisfactory Form of Adjustable Wedge Stop
than that shown in Fig. 20

minimum. Casting C also supports the shoe D and raises it
from the base of the fixture. A tongue is cut on the lower side
of shoe D which fits into a groove in casting C, thereby prevent-
ing the shoe from turning when the nut is tightened or loosened.
Stud E is screwed into the side of the knurled nut and a small
pin F is driven into the shoe. This pin acts as a stop for the

104

JIG DESIGN

stud, preventing the operator from turning the nut more than
is necessary in tightening or loosening.

The adjustable stop shown in Fig. 22 meets practically all
requirements placed on an adjustable stop. It will not slip
back under the pressure of the stop; it will not slip in tighten-
ing; it is dirt-proof; all the parts form integral parts of the jig;
and it will not become loose, due to vibration of the machine,
or spring down under the pressure of the cut, due to unevenness
of the tables of the machines on which the fixture is used. It
can be rapidly operated and is so sensitive that the operator
feels instantly when plunger G is in contact with the work.

X- — JJUIM-

\| WORK j \

' *^^:r — h"

SECTION A-A

Machinery

Fig. 22. Principle of the Final Improvement in the Adjustable
Wedge Stop

The only objection to this design is that so much of the metal
of the base has been cut away that it is seriously weakened,
and the design shown in Fig. 23 is superior in this respect. In
the making of the fixture, difficulties were also encountered in
aligning the holes in bushing A with the holes in casting C,
Fig. 22. This was remedied by making the bushing an easy
fit and adding a small pin D and the round-head screw C, Fig.
23, to keep the bushing from turning or working loose. The
wedge was also jointed and made in two parts, as indicated, in
order to take care of the variations that might occur in drilling

LOCATING POINTS

105

the holes in the bushing A and casting C, Fig. 22, in which the
wedge slides. This practically makes the wedge self-aligning.

Locating from Finished Holes. — If the work to be finished
in the jig has some holes already finished, it is sometimes most
satisfactory to locate the work by these holes, which may be done
by means of studs or plugs similar to the one shown in Fig. 3,
which then enter the holes; preferably, these studs should be
ground and hardened to the standard size of the hole. If the
finished hole should be of a character that varies somewhat in
size, expansion studs with bushings may be used. These studs

Machinery

Fig. 23. The Adopted Form of Adjustable Wedge Stop

may be of a great many different designs and styles, but, as a
rule, they always work on the same principle as the one shown
in Fig. 24. In this, A is the bushing, fitting the finished hole
in the work. This bushing is split in several different ways,
either by having one slot cut entirely through it, and two more
slots cut to within a short distance of the outside periphery, or
by having several slots cut from the top and from the bottom,
alternating, but not cut entirely through the full length of the
bushing. The method of splitting, however, in every case,
accomplishes the same object, that of making the bushing capable

io6

JIG DESIGN

of expansion, so that when the stud J3, which is turned to fit
the tapered hole in the bushing, is screwed down, the bushing
is expanded.

Locating by Keyways in the Work. — Sometimes the work to
be finished in the jig is provided with a keyway or a slot, or with
some other kind of a seat, by means of which it is located on its
component part on the machine for which it is ultimately in-

Fig. 24. Fig. 25. Fig. 26.

tended, and it is always essential that the work be located in
the same way in the jig as it is to be located on the machine
on which it is to go; thus, if the work has a keyway suitable
for locating, a corresponding keyway ought to be put into the
jig, and the work located by means of a key, as shown in Figs.

Fig. 27. Work which is Milled as Indicated at E

25 and 26. Instead of a loose key, a tongue may be planed or
milled solid with the jig, but, as a rule, it is more satisfactory
to have the loose key, as, if it should happen to wear, it is pos-
sible to replace it; and if the width of the keyway should vary
in different lots of the parts made, it is possible, with little ex-
pense, to make a new key to fit the variation, whereas if the
key is made solid with the jig, and found to be either too large or
too small, the trouble of fixing this would be considerably greater.

LOCATING POINTS

107

Common Defects in Jig Design. — The first consideration of
the jig designer should be to determine what degree of accuracy
is essential in the part that is to be produced, and also whether
absolute interchangeability is necessary. This information will
be a guide for the economical production of the jig. The de-
signer must also consider any operations which are to be per-
formed on the work prior to the one for which the jig under
consideration is intended; for while this preliminary machining
may not need to be accurately done, inaccuracy or uniformity
may result in improperly locating the work in the next jig,

-GH

Fig. 28.

Defective Design of Fixture for Holding Piece
shown in Fig. 27

which should be so designed as to locate the part with the re-
quired accuracy.

The locating points of any jig should be such as to allow as
wide a range of inaccuracy on any preceding operation as is
compatible in the part. For example, if the part has to be
turned to, say, a limit of o.ooi inch, it will require more skill and
time than if a limit of 0.005 inch is allowable. Again, as far
as practicable, the portion of the work that requires to be the
most accurate should be used in locating it in the jig for the
succeeding operation. Often a surface is selected to locate
from, which, in consequence, must be machined to an accurate
limit, when accuracy otherwise would be unnecessary. This, of

io8

JIG DESIGN

course, only adds to the cost of production. After considering
the points mentioned, the best method of arranging the details
of the jig, so that it has as few dimensions as possible requiring
absolute accuracy, should also receive attention; that is, the
jig should be as simple as possible, and still be so designed as
to accurately locate the parts to be machined.

In Figs. 28 and 29 are shown two jig designs which will serve
to illustrate these points. The part for which a jig is required
is shown in Fig. 27. In the preliminary machining operation
the work is turned to diameters A and B and to lengths C and
D. The limit of accuracy required on end A is — -^, or any
diameter from i £ f inch as a minimum to i f inch. For end B a

Fig. 29. Fixture which will hold a Number of Pieces, Fig. 27,
properly, even when Diameters of Locating Parts vary

finer limit of —0.002 is necessary, so that this end should be used
as the locating part for the next operation; viz., the milling out
of the slot E which must be central with the part B. A design
such as shown in Fig. 28 is not uncommon for this operation,
and with it fairly accurate results will be secured; but if the
locating diameter on the work is slightly small, say 0.002 inch,
then the forcing of the piece over to one side by the locking
screw A will result in an inaccuracy in the milling operation.
The locating holes B must be the exact size of the locating part
of the work, and unless every piece is a push fit (which is un-

LOCATING POINTS

IOQ

necessary accuracy in the part) the location is not accurate, as
the work is clamped against a small area on one side of the hole
and the point of the set-screw on the other. This can be avoided
by locating the part against V-blocks, as shown in Fig. 29,
which locate each shank central, irrespective of the variations
in their diameters. The construction of this jig illustrates the
points which have been referred to. The V-blocks provide
four lines of contact, and the part is secured very rigidly in a
central position irrespective of the variations in the diameter of
the locating part. This jig, though more expensive than the
one shown in Fig. 28, is quite simple in its construction. A
central slot is machined to a width which need not be to any
particular dimension as the steel V-blocks will be accurately
fitted to this slot. Steel plates are secured to the ends of the

Fig. 30. The Way the V-blocks for the Jig, Fig. 29, are planed

jig after machining the slot as shown. By closing these ends
after the slot is machined, the tool has a clear passage through,
which, of course, would be impossible were the ends cast on.
The V-blocks are planed in one piece, as shown in Fig. 30.
The only important dimension is the width of the block. The
exact position of the V in relation to the sides is immaterial
provided that after the blocks have been sawed off they are
inserted in the slot in the jig with the long or short sides to-
gether. To avoid trouble from this source, one side of the slot
and a corresponding side on the blocks should be marked to
insure the correct insertion of the latter. In the event of a
design requiring the V's to be strictly central with the sides,
the cost would, of course, be increased, as much more care
would be required in machining. The jig shown in Fig. 29 is
for holding three of the pieces shown in Fig. 27 at one time;
this number could be increased as desired.

CHAPTER VI
JIG CLAMPING DEVICES

The clamping devices used in connection with jigs and fix-
tures may either clamp the work to the jig or the jig to the work,
but very frequently the clamps simply hold in place a loose or
movable part in the jig, which can be swung out of the way to
facilitate removing the work from, and inserting it in, the jig.
The work itself is in turn clamped by a set-screw or other means
passing through the loose part, commonly called the leaf.

Types of Clamps. — The simplest form of clamping device is
the so-called clamp, of which a number of different forms are
commonly used. Perhaps the most common of all clamps is
the one shown in Fig. i. This kind of clamp is also commonly
termed a strap. It is simple, cheap to make, and, for most
purposes, it gives satisfactory service. The clamp shown in
Fig. 2 is made on practically the same principle as the one
shown in Fig. i, but several improvements have been intro-
duced. The clamp is recessed at the bottom for a distance 6,
to a depth equal to a, so as to give a bearing only on the two
extreme ends of the clamp. Even if the strap should bend
somewhat, on account of the pressure of the screw, it would be
certain to bear at the ends and exert the required pressure on
the object being clamped. This strap is also provided with a
ridge at D, located centrally with the hole for the screw. This
insures an even bearing of the screw-head on the clamp, even
if the two bearing points at each end of the clamp should vary
in height, as illustrated in Fig. 3. The clamp in Fig. i would
not bind very securely, under such circumstances, and the col-
lar of the screw would be liable to break off, as the whole strain,
when tightening the screw, would be put on one side.

A further improvement in the construction of this clamp
may be had by rounding the under side of the clamping points

CLAMPING DEVICES

III

A, as shown in Fig. 4. When a clamp with such rounded clamp-
ing points is placed in a position like that indicated in Fig. 3,
it will bind the object to be held fully as firmly as if the two
clamping surfaces were in the same plane.

The hole in these straps is very often elongated, as indicated
by the dotted lines in Figs, i and 2. This allows the strap to

Fig. i.

Fig. 2.

be pulled back far enough so as to clear the work, making it
easier to insert and remove the piece to be held in the jig. In
some cases, it is necessary to extend the elongated hole, as shown
in Fig. 5, so that it becomes a slot, going clear through to the end
of the clamp, instead of being simply an oblong hole. Aside
from this difference, the clamp in Fig. 5 works on exactly the
same principle as the clamps previously shown.

Fig. 3.

Fig. 4.

The clamps described may be given a number of different
shapes to suit different conditions. Instead of having the strap
or clamp bear on only two points, it is sometimes necessary
to have it bear on three points, in which case it may be designed
similar to the strap shown in Fig. 6. In order to get an equal
pressure on all the three points, a special screw, with a half-
spherical head like the one shown, may be used to advantage.
The half-spherical head of this screw fits into a concave recess of

112

JIG DESIGN

the same shape in the strap. When the bearing for the screw-
head is made in this manner, the hole through the clamp must
have plenty of clearance for the body part of the bolt.

When designing clamps or straps of the types shown, one of
the most important considerations is to provide enough metal
around the holes, so that the strap will stand the pressure of
the screw without breaking at the weakest place, which naturally
is in a line through the center of the hole. As a rule, these
straps are made of machine steel, although large clamps may
sometimes be made from cast iron.

Fig. 5.

Fig. 6.

Fig. 7.

Fig. 8.

Figs. 7 and 8 show clamps bent to meet the requirements,
and also indicate the application of this type of clamp, the
part shown in cross-section being the work. These clamps are
commonly used for clamping work in the planer and milling
machine, but are also frequently used in jig and fixture design.

The screws used for clamping these straps are either standard
hexagonal screws or standard collar-head screws. When it is
not necessary to tighten the screws very firmly, thumb-screws
are frequently used, especially on small jigs.

Sometimes the strap or clamp is arranged as shown in Fig. 9,
the screw passing through it at the center and bearing upon
the work, either directly, as indicated, or through the medium
of a collar fitted to the end of the clamping screw, as shown in

CLAMPING DEVICES

1*3

Fig. 10. This type of clamping arrangement is commonly used
for holding work in a drill jig when one screw is sufficient. The
strap used in this type of arrangement can be improved upon
by making it in one of the forms shown in Fig. 1 1 . Here the ends

Fig. 9. Clamping Strap for Open-end Jigs

of the straps are slotted in various ways, so as to make it easy
to rapidly remove the strap when the work is to be taken out
of the jig. Fig. 12 illustrates a method which is not often found
in use. This type of clamp is adapted to box jigs; it has the

Fig. 10. Common Form of Clamps with One Binding Screw

advantage of being easily removed, which is accomplished by
sliding it longitudinally. By glancing at the detailed view to
the right, which shows the end of the clamping bar and its
retaining grooves, the way in which it is held in place and re-
moved will be clearly understood. Figs. 13 and 14 show clamps

JIG DESIGN

which are very much alike, but that of Fig. 14 is simpler
and more rapidly operated when the work is to be removed.
When the clamp is slotted as shown in the plan view of Fig. 14,
fixed studs may be used instead of the swinging bolts.

f-\ ,ft?> \ 1

\ \ I

( — ""^1 A ( — ^

:"r:

c j Y *• '

:"--

H 5H-X3

_J f U

Fig. ii. Types of Clamping Straps

The type shown in Fig. 15 is often found in machine shops,
on milling fixtures, drill jigs, lathe fixtures, etc. The clamp
and bolts can be removed by loosening the nuts and pulling out
the slip washers which allow the nuts to pass through the large

Fig. 12. Clamp Adapted to Box Jigs

holes. Fig. 16 illustrates a method which is commonly used
on milling fixtures when light milling is to be done. The design
of clamp shown in Fig. 17 is not frequently seen in use, as it is
a method which a mechanic will not use if he can see another
way out of it; but at times it is found almost impossible to use
a clamp of a different type.

CLAMPING DEVICES

A style of clamp that is somewhat similar to the one illustrated
in Fig. 12 is shown in Fig. 18. In this case, however, two
clamping bolts are used and the clamp is removed from the end
of the jig. This is a good as well as a quick method of clamp-
ing work in open-end drill jigs. Fig. 19 illustrates the use of
bolts only, for holding down work. The illustration is self-

Fig. 13. Clamp with Swinging Bolts

explanatory. Fig. 20 shows a good design of clamp for holding
work in a milling fixture. It binds the work both horizontally
and vertically and is the very best type for its purpose when
it can be used.

Fig. 14. Easily Removable Clamp

Hook-bolts. — The hook-bolt shown in Fig. 21 is better
adapted for some classes of work than any other clamping de-
vice. At the same time, it is very cheap to make and easily
applied. The bolt A passes through a hole in the jig, having a
good sliding fit in this hole, and is pushed up until the hook or

Il6 JIG DESIGN

Dimensions of Collar-head Screws used on Jigs

REQUIREMENTS

Machinery, 2V. F.

St'd No. of

Threads per

Inch

Me
M

o. 260

0.440

0-53°
0.620
o. 710
0.700

0.880

1 .060

Ha
Me
Me

JS2

Me
Hie

I Me

18
16
14
13

12
II
IO

Dimensions of Shoulder Thumb-screws used on Jigs

T S~*\

L( T

< IIIIIHHIIIII

Me
!4
Me
%

l/2

Me
I

IM
iM

i1/^
i5/^

!H6

i/3/ie
'Me

Me
Me

t \ /
n\^

ACCORDING TO

« ' yi

REQUIREMENTS
, ,

f i ±i| illllllll

J Machinery, N.Y.

Dimensions of Wing- or Thumb-nuts for Jigs

I1 Me
2

Me
H

iMe

Me
Me

CLAMPING DEVICES

117

head B bears against the work, after which the nut is tightened.
When great pressure is not required, the thumb- or wing-nut
provides a satisfactory means for tightening down upon the work,
and permits the hook-bolt to be applied more readily. The
thumb- or wing-nut is preferable to the knurled nut, shown in
Fig. 24, which sometimes is used. It is possible to get a better

Fig. 15. Clamp with Slip Washers beneath Nuts

Fig. 1 6. Method used for Light Work

Fig. 17. Clamping Method not to be Recommended

grip and to tighten the bolt more firmly with a wing-nut than
with a knurled nut. When the work is removed from the
jig, using the hook-bolt clamping device, the nut is loosened
and the head or hook of the bolt is turned away from the work,
thus allowing it to be taken out and another piece of work to
be placed in position. The hook-bolts are invariably made of
machine steel. Fig. 25 shows an application of a bent hook-
bolt. Generally speaking, the type shown in Fig. 21 is better

JIG DESIGN

suited to its purpose, because the bearing point on the work is
closer to the bolt body.

Screw Tightening Devices. — In a box jig, or a jig where the
work is entirely, or almost entirely, surrounded by the jig, the
work is easily held in place by set-screws which are used when-

Fig. 18. Simple Clamping Method

Fig. 19. Clamping by Set-screws in Open-end Jig

Fig. 20. Clamps that hold the Work Firmly in place

ever great clamping pressure is required, the square head allow-
ing the use of the wrench. Sometimes screws of this kind may
be tightened enough for the purpose by hand if a pin is put
through the head of the screw, as shown in Figs. 22 and 23.
This means is used not only when great pressure is not necessary,
but also when the work is liable to spring if the screws are

CLAMPING DEVICES

IIQ

tightened too hard. In such a case, if a pin is inserted, it is
obvious that the screw-head is not intended for a wrench, but
that the pin is intended for getting a good grip by the hand
for tightening the screw, without resorting to any additional
means. Usually it is not possible to use an ordinary machine
wrench on such a screw. Wing-nuts are generally most
satisfactory for jigs where only a light binding pressure is
required.

Wing-nuts are used on hook-bolts or swiveling eye-bolts,
when a comparatively light pressure is required. The thumb-

Fig. 21. Fig. 22. Fig. 23. Fig. 24.

Fig. 25. Hook-bolt Method of Clamping

or wing-nut is preferable to a knurled nut, as it gives a better
grip and makes it possible to tighten the bolt more firmly. The
dimensions of an excellent design of handwheel for use on jigs, etc.,
are given in an accompanying table. These wheels have a rather
long stem or hub which provides a good length of thread and
brings the grip or handle far enough from the jig body to prevent
the fingers or knuckles from striking it. The "star" design of
handle also permits a good grip. By having the casting solid,
these handwheels can be tapped out for any size thread, or a

I2O

JIG . DESIGN

plain hole can be drilled when it is desired to attach the handles
to round stock.

If screws are to. be firmly tightened without the use of a
wrench, the method of using a pin through the screw-head
should be used only on large fixtures, where the pin is f inch

Fig. 26. Pin used as Handle for Binding Screw

in diameter and requires the use of both hands, an application
of which is shown in Fig. 26. On smaller sizes of fixtures where
the pin is about J inch in diameter by 4 inches long, and must
be used with one hand, the pressure is concentrated across the

Fig. 27. Hand Knob for Binding Screw

palm of the hand, and if the fixture is used frequently it is
likely to develop a sore spot.

In the case of the hand knob shown in Fig. 27, however, it
is evident that the pressure is distributed over the palm of the
hand, and therefore the likelihood of producing a sore is much
less. Tables of sizes of two different types of knobs for differ-
ent classes of fixtures are given herewith.

CLAMPING DEVICES
Dimensions of Latch Nuts

121

Me
H
He
Hi

Me
Me
M

Star Handwheels for Jigs

Me
Me

Me
Me
Me

Me
Me

Dimensions for Cast-iron Knobs

H=RADI

!< c — >|

U.. D -J<--E-*!

I
I

l_:i

H'h

Machinery

Size

'Me

iH
H

9*2

I Me

H
I Me

«2

i Me

2->i

I Me
H
Me

I'/i

iH
W

122

JIG DESIGN
Dimensions of Jig-screw Latches

3W
4*

H
94
N

i
154

Me
H

Me
Me

Dimensions of Regular Thumb-screws

ACCORDING TO
P REQUIREMENTS

Machinery, N.Y.

Me
H
Me
%
Me
H

I M

Hi
Mi

Me
Ms

Dhnensions of Thumb-screws with Wide Grip

ACCOROINQ TO

REQUIREMENTS

Machinery ,N.T

Me
X

Me
H

Me
%
Me
H

2
2J4

Me
Me
Me
Jfe

The questions naturally arise, how much pressure can a man
exert with his fingers in operating a knurled-head screw, how
much pressure can he develop with a screw and hand knob,
and how much pressure can he exert in operating a screw with a
pin through it? It is quite safe to say that for continuous
operation on jigs or fixtures all that can be depended upon with
a knurled-head screw is to bring the screw up to steady the
work, but, with a screw and pin through it, it is not uncommon

CLAMPING DEVICES

123

to bend the pin. With a hand knob the amount of pressure is
doubtful and depends largely upon the position of the screw,
which governs the grip obtainable on the knob.

Swinging Leaves. — The elementary principles involved in
the swinging-leaf clamping construction are shown in their sim-
plest form in Fig. 28. Loose leaves which swing out, in order

Fig; 28. Principle of Commonly used Clamping Method

Fig. 29. Another Common Design of Jig Leaf

A A-

+ |

QETI /

I i

b-----J

-J1_L/

•j i -

Fig. 30. Clamping Device for Drill Jig Leaf

to permit the work to be inserted and removed, are usually
constructed in some manner similar to that shown in Fig. 29,
in which A represents the. leaf, being pivoted at B and held by
a pin at C, which goes through the two lugs on the jig wall and
passes through the leaf, thus binding the leaf and allowing the

124

JIG DESIGN

tightening of the set-screw D, which bears against the work.
The holes in the lugs of the castings are lined with steel bush-
ings in order to prevent the cast-iron holes from being worn
out too soon by the constant pulling out and putting in of the
pin. This kind of leaf, when fitted in nicely, is rather expensive,
but is used not only for binding purposes, but also for guiding
purposes, making a convenient seat for the bushings. If leaves
are fitted well in place, the bushings in the leaves will guide the
cutting tools in a satisfactory manner.

Another method of clamping down the leaf is shown in Fig. 30,
in which A is a thumb-screw, screwed directly into the wall B of
the jig, and holding the leaf C down, as indicated. To swing the

— B—

Fig. 31. Eye-bolt used for Clamping Drill Jig Leaf

leaf out, the thumb-screw is turned back about a quarter of the
turn, so that the head of the thumb-screw stands in line with
the slot in the leaf, this slot being made wide and long enough to
permit the leaf to clear the head of the thumb-screw. This is a
very rapid way of clamping, and is frequently used. The lower
side of the head of the screw will wear a long time before the head
finally comes in line with the slot when binding. It can then
easily be fixed for binding the leaf again when standing in a
position where the head of the thumb-screw is at right angles to
the slot, by turning off a portion of the head on the under side

CLAMPING DEVICES

125

The size of these thumb-screws is made according to the strain
on the leaf and the size and design of the jig. No standard
dimensions could be given for this kind of screw.

The hinged bolt or latch bolt, shown in Fig. 31, is also com-
monly used. Here A represents an eye-bolt, which is connected
with the jig body by the pin B. The leaf or movable part C
of the jig is provided with a slot in the end for the eye-bolt,
this slot being a trifle wider than the diameter of the bolt.
The threaded end of the eye-bolt is provided with a standard
hexagon nut, a knurled-head nut or a wing-nut, according to
how firmly it is necessary that the nut be tightened.

When the leaf is to be disengaged, the nut is loosened up

Fig. 32. Detail Designs of Hinged Leaves

enough to clear the point at the end of the leaf, and the bolt is
swung out around the pin B, which is driven directly into lugs
projecting out from the jig wall, a slot being provided between
the two lugs, as shown, so that the eye-bolt can swing out
with perfect freedom. At the opposite end, the leaves or loose
parts of the jig swing around a pin the same as in Fig. 29, the
detailed construction of this end being, most commonly, one of
the three types shown in Fig. 32. It must be understood that
to provide jigs with leaves of this character involves a great
deal of work and expense, and they are used almost exclusively
when one or more guide bushings can be held in the leaf.

Quite often drill jigs have a bushing plate in the form of a
leaf which swings on a hinge out of the way so that the piece

126

JIG DESIGN

to be drilled can be put in place in the jig. This requires a
locking device which can be depended upon to hold the bushing
plate exactly in place while drilling. The locking device shown
in Fig. 33, and also shown applied to a jig in Fig. 34, answers
this purpose admirably. To open the jig so as to put in the
piece to be drilled, all that is necessary to do is to push the

Fig. 33. A Jig Locking Trigger

button on the end of the lock trigger and lift the leaf up. When
the piece is in place in the jig, the leaf is again pressed down
into place. The pressure springs the locking device, and the
trigger grips the pin shown. The part of the trigger which

Fig. 34. Locking Device in Fig. 33 applied to Jig

fits against the pin should taper slightly. This makes it hold
much more tightly, and also takes up what little wear there
may be on it. The device can be fitted to a great variety of
jigs and fixtures. It is very simple and inexpensive to make,
is quick and simple to operate, and is positive in its action.

A hinged jig cover may also be conveniently held in place by
means of a spring latch of the form shown in Fig. 35, which is

CLAMPING DEVICES

127

semi-automatic in its action. In this illustration, the body of
the jig is shown at A and the hinged cover at B. This cover
swings on the pivot C and drops onto the latch D which takes
the place of the locking screw arrangement shown in Fig. 36,
and which shows an application of the principle illustrated in
Fig. 30. In cases where the cover is merely used to carry bush-
ings, a latch of this kind is entirely satisfactory, although it
is not recommended for use on jigs where screws for holding
down the work are carried by the cover. The method of using
is evident from the illustration. To swing the cover clear of

1 K-i-

~~]

Lra

i
i

! V

o <r!~j

,-tg

-4-

n i

1 L — \-

}

D — -

s^sc
B

y /

-c

! !

\ j

iff.

Fig. 35. Jig with Cover held by Spring Latch

the work in the jig, the latch D is pushed back in the direction
of the arrow. After the cover has been raised, the latch springs
back into place ready to catch over the top of the cover, when
it is dropped back onto the jig. When the cover is dropped,
the latch catches it automatically, requiring no attention from
the operator.

A number of applications that vary in details only are shown
in Figs. 37 to 40. Fig. 37 shows the style of clamp that is used in
connection with box drill jigs when it is desired to support a part
to be drilled on two points. As will be seen, these two bearing
points are self-adjusting. The design of Fig. 38 is generally
used when it is desired to support the work in two places in

128

JIG DESIGN

an open-end drill jig. Figs. 39 and 40 show types which are
quite similar, but there are many cases where one type can be
used to advantage and not the other. For instance, the clamp,
Fig. 39, is intended for box jigs, but the type shown in Fig.
40 could not be used for such a jig, because the latter is alto-
gether too slow. However, its advantages over Fig. 39, in case

Fig. 36. Jig Cover Locked by Quarter-turn Screw

i ,' O\ i

Fig. 37- Jig Cover with Two-point Self-adjusting Clamp

it is desired to have an open-end jig, are apparent. The relation
of the first cost of a jig to the quantity of work to be done is a
factor which sometimes makes a jig which is not perfect, from a
purely mechanical standpoint, more desirable than one which
represents better design, but greatly increased cost.

The ordinary jack-screw is employed quite commonly as a
clamping device in drill jigs, but the objection to its use is that,

CLAMPING DEVICES

129

not being an integral part of the jig, it is very apt to get lost.
In Fig. 41 are shown two simple devices working on the same
principle as the jack-screw, but having the advantage of being
connected to the jig by the pin shown at B. At A, a set-screw
screws directly into the end of the eye-bolt, and at C a long

Fig. 38. Compensating Two-point Clamp

Fig. 39. Non-compensating Two-point Clamp

Fig. 40. Alternative Design, Similar to that in Fig. 39

square nut is threaded on the eye-bolt. These nuts must be
made of special length, and be made up especially for this pur-
pose. The eye-bolts are fastened, as shown, directly to the wall
of the jig, and the set-screw or nut is tightened against the work.
The eye-bolt can be set at different angles to suit the work,

I30

JIG DESIGN

thereby providing a clamping device which may be said to
possess double adjustment. This device makes a very con-
venient clamping arrangement. It works satisfactorily and has
the advantage of being easily swung out of the way.

Wedge or Taper Gib. — The principle of clamping work in the
jig by means of a wedge or taper gib is shown in Fig. 42 and
two applications are illustrated in Figs. 43 and 44. In Fig. 43,

Fig. 41. Clamping Devices Working on the Jack-screw
Principle

Fig. 42. Simplest Application of Wedge Clamp

the work is located between the wedge A and the wall B of the
jig and pressed against the wall by the wedge, which can be
driven in by a hammer, or screwed in place when the jig is
constructed as shown. It is preferable to have the wedge screwed
in place, as it is then less likely to loosen by the constant vibra-
tions to which it is subjected, and at the same time the wedge

CLAMPING DEVICES

is less likely to get lost, being an integral part of the jig. The
ear for the screw may be placed in any direction in regard to
the gib, as indicated by the dotted lines in the end view of
Fig. 43. This tightening device is, in particular, adapted to
work of dovetail shape, as shown in Fig. 44. In this case the
wedge is made similar to the common taper gib used for taking
up the wear in dovetail slides. It is sometimes of advantage
to relieve the bearing surface opposite the wedge, as shown in

Fig. 43. Wedge or Taper Gib used for Clamping

Fig. 44. Wedge for Clamping Dovetailed Work

dotted lines in Fig. 43, in order to provide two distinct bearing
points, which prevent the work from rocking. The hole in the
ear of the gib, through which the screw passes, must be oblong,
so that when the screw is adjusted, and the gib moved in or
out, there is ample allowance for the sidewise movement of the
ear, due to the taper of the gib.

If it is required to get a bearing on two points of a surface
that is likely to vary in its dimensions, a yoke can be used,
designed on the principle of that shown in Fig. 45. In the

JIG DESIGN

engraving, A is the work to be clamped, and B is the yoke which
fits into a slot in the center of the strap or clamp C. The yoke
is held by a pin D, around which it can swivel to adjust itself
to the work. It is evident that the amount of pressure at the
two points E and F will be equal, or at least near enough so
for all practical purposes, even though the screws at the ends
of the strap may not be equally tightened. In this device the

64^6 n

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Fig. 45. Equalizing Clamp

Fig. 46. Eccentric Clamping Bolt

pin D takes the full clamping strain, and should therefore be
designed strong enough, and the strap, which is weakened by the
slot and the hole in the center, should be reinforced, as indi-
cated, at this place. It is preferable to have spiral springs at
each end of the strap to prevent the strap from slipping down
when the work is taken out. The strap may be made either of
cast iron or machine steel, the yoke being made of machine
steel.

CLAMPING DEVICES

133

Eccentric Clamping Arrangements. — Eccentric clamps and
shafts for binding purposes are often used. In Figs. 46 and 47
are shown two applications of the principle of the eccentric
shaft. In Fig. 46 the eccentric shaft A has a bearing at both
ends, and the eye-bolt B is connected to it at the center and is
forced down when the eccentric shaft is turned. This causes
the two end points of the clamp C to bear on the work. This
clamping arrangement has a very rapid action and gives good
satisfaction. The throw of the eccentric shaft may vary from
TV inch to about J inch, depending upon the diameter of the
shaft and the accuracy of the work. In cases where it is re-

Fig. 47. Another Example of Eccentric Clamping Bolt

quired that the clamp should bear in the center, an arrangement
like the one shown in Fig. 47 may be used. Here the eccentric
shaft A has a bearing in the center and eye-bolts B are con-
nected to it at the ends. As the eccentricity is the same at
both ends, the eye-bolts or connecting-rods will be pulled down
evenly when the lever C is turned, and the strap D will get an
even bearing on the work in the center. If the force of the
clamping stress is required to be distributed equally at differ-
ent points on the work, a yoke like that shown in Fig. 45 may
be used in combination with the eccentric clamping device
shown in Fig. 47.

When it is essential that strap D should also be used for locat-

134

JIG DESIGN

ing purposes, necessary guides must be provided for the strap,
so as to hold it in the required position. These guiding arrange-
ments may consist of rigid rods, ground and fitted into drilled
and reamed holes in the strap, or square bars held firmly in the
jig, and fitted into square slots at the ends of the strap. The
bars may also be round, and the slots at the ends of the strap
half round, the principle in all cases remaining the same; but
the more rigid the guiding arrangement is, the more may the
accuracy of the locating be depended upon.

The ordinary eccentric lever works on the same principle as
the eccentric rods just described. There are a great variety of
eccentric clamping devices, but they are not as commonly used

Figs. 48 and 49. Cams or Eccentrics used for Clamping

in present-day jig design as they were a few years ago. The
eccentric clamping levers, however, provide good and rapid
clamping action. In Fig. 48 is shown one especially intended
for clamping finished work. It is not advisable to use this kind
of lever on rough castings, for the reason that the latter may
vary so much that the cam or eccentric would require too great
a throw for rigid clamping to suit the rough castings. The
extreme throw of the eccentric lever should, in general, not
exceed one-sixth of the length of the radius of the eccentric
arc, if the rise takes place during one-quarter of a complete
turn of the lever. This would give an extreme throw of, say,
J inch for a lever having i| inch radius of the cam or eccentric.
It is plain that as the eccentric cam swivels about the center Ay

CLAMPING DEVICES

the lever being connected to the jig with a stud or pin, the face
B of the cam, which is struck with the radius R from the center
C, recedes or approaches the side of the work, thereby releasing
it from, or. clamping it against, the bottom or wall of the jig.
The lever for the eccentric may be placed in any direction, as

Fig. 50. Application of Clamping Cam

indicated by the full and dotted lines in Fig. 48. In Fig. 49 is
shown another eccentric lever, which is used frequently on small
work for holding down straps or leaves, or for pulling together
two sliding pieces, or one sliding and one stationary part, which
in their turn hold the work. These sliding pieces may be

Fig. 51. The " Gripping Dog " Method of Clamping

V-blocks or some kind of jaws. The cam lever is attached to
the jig body, the leaf, or the jaw, by a pin through hole A.
The hook B engages the stud or pin C which is fastened in the
opposite jaw or part, which is to be clamped to the part into
which the pin through hole A is fastened. The variety of
design of eccentric cam levers is so great that it is impossible
to show more than the principles, but the examples shown

136

JIG DESIGN

embody the underlying action of all the different designs. An
elementary application is shown in Fig. 50.

Irregular shaped castings which must be machined often
present no apparently good means of holding by ordinary grip-
ping appliances for drilling, shaping, or milling. In such cases
a gripping dog, as illustrated in detail in Fig. 51, may be used.
The base block C of the dog is slotted to receive jaw D, which
is fulcrumed on a cross-pin. In the tail of the dog is threaded
a set-screw £, and by turning in this set-screw the jaw is caused
to "bite" inward and downward at the same time, firmly grip-

SLIDING V-BLOCK.

Fig. 52. Work Held by V-clamps

ping the casting and forcing it down on the table. A backstop
F is bolted behind each dog, so that there is no chance for slip-
ping away from the work.

Applications to Jig Design. — The preceding description and
illustrations indicate the principles embodied in jig clamping
devices. The following typical illustrations show a number of
applications that are merely modifications of the various methods
already reviewed. Most of the devices described may be
quickly operated, the purpose being to show a collection of
efficient designs that will hold the work securely. They possess
the further advantage of being relatively simple, so that the
jigs can be made at a moderate cost in all cases where there are

CLAMPING DEVICES

137

a sufficient number of pieces to be machined to warrant making
a good tool.

WEDGE
\

ADJUSTING SCREW

STING SCREW

Fig. 53. Sliding Clamps

Fig. 54. Hinged Cover with Locking and Ciimp Screw

A method of holding a piece of work with an oval-shaped
flange is shown in Fig. 52. This piece is held between V-blocks,
one of which is stationary while the other is moved by a screw.

JIG DESIGN

A pilot on the end of the adjusting screw enters a hole in the
V-block, the two members being held together by a pin which
fits in a groove in the pilot. The movable V-block is held to
the body of the jig by two steel straps. Fig. 53 illustrates, in
the upper view, another method of attaching a screw to a slid-
ing clamp member. In this case, the sliding piece is used for
forcing the work down into place. This screw runs in a tapped
hole in a stationary part of the fixture, while the collar at the
end of the screw fits into the movable wedge to push it forward
or draw it back. The lower view shows a movable clamp

HINGED COVER

ECCENTRIC BINDER

LT^

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L_ A-

[ ,>~: ,

' ' /

WORK

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Fig. 55. Hinged Cover with Floating Stud

member that has a tapped hole to receive the adjusting screw.
Here two collars on the screw are located at each side of a boss
on the fixture and the adjustment is obtained by the screw
turning in the tapped hole.

Two examples of hinged covers are shown in Figs. 54 and 55.
The cover shown in Fig. 54 (same principle as in Figs. 30 and 36)
is held in place by a locking screw, while the work is secured by
a set-screw carried by the cover. The hinged cover illustrated
in Fig. 55 is provided with a floating stud that secures the
work, the cover which carries the stud being held in place by
an eccentric binder with a hook which slides under the pin A.

CLAMPING DEVICES

139

This provides a very quick-acting jig. The lug B at the oppo-
site end of the cover prevents it from swinging back too far
and breaking the hinge.

Fig. 56 shows the application of a bell-mouthed bushing,
which is screwed down onto the hub of a lever, thereby locating

Fig. 56. Bell-mouthed Screw Bushing

Fig. 57. Slip-on Knob for Clamping

the work and at the same time providing a guide for the drill
which is to operate upon it. The objection to this type of
bushing is that it requires an extra long drill, and if made with
two sizes of holes, as shown, particular care will have to be taken
in using small drills, to prevent breaking a number of them.

140

JIG DESIGN

Another objectionable feature of this clamping device is that
chips work into the threads and prevent turning the bushing
easily which also shortens the life of the thread. This difficulty
can be overcome, however, by not tapping the hole all of the way
through, as indicated at A\ by counterboring the hole at the
top marked B; and then grinding the pilot C and shoulder D
on the bushing to a snug running fit. The bushing is then held
true and chips are excluded from the thread. The average
tool designer, nevertheless, avoids screw bushings whenever pos-

Fig. 58. An Improvement on the Screw Bushing

sible, but such bushings are frequently selected after careful
consideration because of their neat appearance and effective
operation.

Fig. 58 shows a clamping device which, although a little more
expensive than a screw bushing, would probably pay for itself
in saving the breaking of drills, as the bushing on this jig can be
made shorter and with a one-size hole. The screw A swings
the lever B about pin C and pushes down the bushing D which
is a slip fit in the body of the jig.

A rather unusual method of clamping is illustrated in Fig. 57,

CLAMPING DEVICES

141

where it will be seen that the hand knob has the thread milled
out to the edge to give a "slip over and twist" motion for clamp-

Fig. 59.

Fig. 60.

Fig. 61. Binding Screw Pivoted in Clamp

ing the work. Practically the same idea is illustrated in Fig. 59,
except that a wrench handle is provided in this case to facili-
tate tightening. Both of these arrangements enable work to

142

JIG DESIGN

be tightened in the fixture with great rapidity. Fig. 60 shows a
special nut for a box wrench, the purpose of which is to permit
lifting the wrench off the "hex," and moving it back for a new
grip. The round part of the nut serves to keep the wrench in
place to be slipped back onto the hexagon nut, while the pin at
the top of the nut makes the wrench an integral part of the
fixture, so that it cannot get lost.

Two unusual examples of jig and fixture design are illustrated
in Figs. 6 1 and 62. The distance that the clamp had to be

1 1

1 r

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1 i
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! i

Fig. 62. Quick-releasing Clamping Arrangement

raised in removing the work from between the V's of these
fixtures made it desirable to provide some method of releasing
the clamp more quickly than by turning the screw back through
the necessary distance. The way in which this was accom-
plished is clearly shown in the illustrations, and will be seen to
consist of loosening the screw and then swinging the block
which carries the screw on the pivot A , the direction being indi-
cated by the arrow. This moves the screw off its bearing on

CLAMPING DEVICES

143

the casting in the case of the jig shown in Fig. 61, while in Fig.
62 the binding screw is removed from the clamp. The clamp
shown in Fig. 62 has been cut away at B to permit the point of
the screw to clear it; a spring-pin holds the clamp against the
screw at all times.

Fig. 63 shows a hinged cover with the clamp attached to it.
This is a convenient arrangement to remember when consider-
ing the design of jigs and fixtures. The clamp and cover are

HINGED COVER

fow

. V-' /III

| L __ 1

CLAMP

Fig. 63. Hinged Cover with Attached Clamp

held by the same pin and both parts are swung out of the way
at the same time by means of the corner of the clamp, which
catches on the hinged cover at B. The design is such that the
fixture has sufficient clamping range when the cover is held in
place by the screw C. The clamping is effected by means of
the screw in the cover which forces the clamp down on the
work. Fig. 64 shows a clamp beveled at the end to pull the
work down flush and push it into the V at the same time. The
clamp is tightened by a screw and a spring forces it open when

144

JIG DESIGN

the screw is loosened. This type is often used when it is desir-
able to keep the clamp out of the way of the cutter.
Two examples of the use that can be made of cams are shown

Fig. 64. V-block Clamp

Fig. 65. Cam Clamping Device

in Figs. 65 and 66. The device shown in Fig. 65 is simply an
eccentric stud operated by a handle. This device pushes the
clamp against the work; a hole is drilled in the clamp to slide

CLAMPING DEVICES

145

over the guide pin mounted in the frame of the jig. Fig. 66
shows a cam for operating a sliding V, the method being evi-
dent from the illustration. Another form of quick-acting clamp
is shown in Fig. 67. This device consists of a bar that is hinged
on a stud at one end and has a slot cut in the opposite end to
slip under a second stud. The screw that clamps the work
also serves to secure the clamp in place.

A simple form of gang milling fixture is shown in Fig. 68, where
the different pieces are clamped by separate screws held in a
bar that can be swung out of the way to enable the work to be

Fig. 66. Another Application of a Cam Clamping Device

removed from the jig. This also makes it possible to brush the
chips out at the side of the jig.

In Fig. 69 is shown a clamping device that has been found
useful on large work. It consists of four arms A with the
ends bent to a right angle and knurled so as to hold the work
firmly in place. These arms are pivoted on the stud B and
their action is guided by the blocks C. The spring handle E
is pinned to the shank of the stud, and the upper edge of the
handle is beveled to fit the rack D, which is fastened to the
side of the base. By turning the handle in the direction indi-

146

JIG DESIGN

cated by the arrow the work is securely clamped and, if neces-
sary, ordinary straps may be added for holding the work.

When making tools for thin castings of odd shapes, it is often
desirable to use an adjustable clamping device that can be

SWIVEL STUD

LOCKING STUD

Fig. 67. Quick-acting Clamp of Simple Design

UJ UU LLJ UJ UJ
BINDING SCREWS WORK

SWINGING BAR

Fig. 68. Simple Form of Gang Milling Fixture

easily moved out of the way when reloading the fixture.
Such a floating clamp is shown in Fig. 70, where the piece of
work to be drilled was properly located and clamped, with the
exception of one arm £, for which no ordinary clamp could be
used. By pushing the support A down against the work and

CLAMPING DEVICES

clamping the strap B, the work is held tight without springing
it; and by tightening the nut C the clamp is held in place by
the bunter and the work is securely supported. When reload-
ing the fixture, the clamp is brought out of the way by means of
the handle D.

In Fig. 71 is shown a small clamping device used when drill-
ing the rivet holes through the beading A and the plate B. The
steel bracket C is fastened by screws to the side of the fixture.
The front face of the clamp bracket is used as a stop for the plate

SECTION X-X

Machinery

Fig. 69. Clamping Device for Holding Large Work

and the beading, and the clamp D with a small hole drilled in
one end is fitted loosely in the milled slot in the bracket. The
set-screw is located a little higher than the hole in the clamp
and by a few turns of the screw the clamp is brought down
against the work and forces the beading up against the stop
ready to be drilled.

Spring bunters are often used in designing fixtures where
adjustable supports are necessary, and the form of bunter shown
in Fig. 72 has proved very efficient. The bunter A and the
binder B fit freely in the holes in the casting. The bunter is

148

JIG DESIGN

•P

II
«2

a w>

I"
Jl

CLAMPING DEVICES 149

slightly tapered and a tapered flat is milled on one side of
the binder. When the fixture is loaded the spring D forces the
hunter up against the work, and by means of the cam C the
binder is pulled outward and holds the bunter firmly in place.
The double taper on both bunter and binder makes it impos-
sible to press the bunter downward away from the work.

Conclusion. — When designing clamping devices, as few oper-
ating screws or handles should be used as will accomplish the
desired result, for it takes considerable time to turn a screw
one or two revolutions four or five thousand times a day, which
is an average number of operations for many jigs. Making
the screw with a double or triple thread is sometimes done to
advantage in decreasing the number of turns necessary to re-
lease the piece. Jig lids should be hung on taper pins in order
that wear in the hinge may be compensated for and the resulting
inaccuracy due to the lost motion in the hinge prevented. The
included angle of taper on hinge pins should be only one or two
degrees and the pins should be spirally grooved to within f inch
of each end, in order to hold oil for lubricating the hinge after
the pin is driven in. The hinge pin should be a tight fit in the
central portion of the hinge, which is usually the jig body, and
a bearing fit in the ears of the lid. In this manner the greatest
wearing surface possible is obtained.

All clamping screws and similar parts should be long enough
and so located as to be conveniently taken hold of to operate,
and of sufficient size to prevent hurting the operator's hands on
account of the pressure necessary to manipulate them. The
screws should be located so that they will resist the tilting
action of the block, and the dowel pins should be fairly close
to the screws and of liberal dimensions in order to resist the
shearing strains to which they will be subjected. When clamp-
ing or locating the work in the jig, it is essential to have the
clamping pressure exerted in a direct line against some solid
point of support to prevent the tilting tendency, and the thrust
should also come on such a point of the work that it will be
resisted by solid metal, as the pressure of a screw is frequently
underestimated by both the designer and the operator of the

150 JIG DESIGN

jig, with the result that the work will frequently be sprung by
the clamping device and drilled in this position, which would
naturally spoil the accuracy of the location of the hole after the
work was released from the jig and had expanded back to its
normal shape.

It should be further borne in mind when clamping rough cast-
ings in a fixture, that they can be supported only on three points,
and adjustable stops should be placed on the fourth point of
the support and also under any weak portions of the piece
through which holes are to be drilled or machining operations
are to be performed, in order to resist the springing action of
the cutter. Posts in which clamping and locating screws oper-
ate should be 01 liberal proportions and should not project above
the fixture body any further than is necessary in order to keep
down the tilting action to a minimum; and all handles for
clamping devices should be so located that they will not be
awkward to operate.

CHAPTER VII
EXAMPLES OF DRILL JIG DESIGN

As jigs and fixtures are now used wherever machines and tools
are constructed, the number of designs in use is practically
endless, although a great many of the simpler jigs are con-
structed on the same general principle and differ chiefly in
regard to form. There are, however, many distinct types which
have been developed to handle different classes of work to the
best advantage. Since the jig or fixture is designed around the
part for which it is intended, the form and size naturally vary
accordingly; but aside from such changes, there are many
details for insuring accuracy of location and rapidity of clamp-
ing or releasing, which give the designer an opportunity for
the display of judgment and ingenuity in producing a jig that
is effective, and at the same time not unnecessarily complicated
and expensive. In order to illustrate the relation between the
work to be done and the design of the jig or fixture for that work,
this chapter and those which follow will be confined largely to
illustrated descriptions of designs taken from practice. In
selecting these 'designs, the object has been to show as many
types of jigs and fixtures as possible.

Drill Jig having Automatic Locating Devices. — In Fig. i
is shown a combination flywheel and driving pinion A which
is to be drilled and tapped for four hollow-point set-screws as
shown. All the surfaces marked with dotted lines, as well as
the bore, are finished before the wheel comes to the drilling
machine. The problem was to construct a jig by which any
unskilled laborer or boy could drill and tap these wheels quickly
and correctly without any previous laying out of the holes.
The jig had to be constructed so that it would be practically
impossible to make any mistake in drilling when the work was
properly clamped.

10 J

151

152

JIG DESIGN

The jig shown in Fig. 2 fulfills all these conditions and gives
very good results. It consists of a cast-iron angle-plate base B,
which is fastened upon the drilling machine table. A bracket C
is fastened to this base by countersunk fillister-head screws.
This bracket, which is of U-shape, is provided with a stud L
fitting into the finished bore of wheel A. The two arms of the
U-shaped bracket serve as supports for the drill guides M.
At one side the pin P passes through bracket C, while the oppo-
site side of C is provided with an indentation to receive the
pin N which connects the drill guides M . Pin N is held in

Machinery

Fig. 1. Combination Flywheel and Driving Pinion

place by headless set-screws 61 which also hold the drill guides
to pin P as shown. One end of pin N forms a handle by means
of which the guides may be conveniently swung out about
pin P as a fulcrum. Bracket C fits tightly between drill guides
M at both ends, thus holding them firmly in place. A screw 0
having its center located somewhat above the center of pin N
prevents this pin and also the drill guides from coming up with
the drill, and breaking the latter. Bracket C is provided with
a slot in which slides a rack D, a detail view of which is shown
at F, which is provided with teeth of the same pitch as those
in pinion A that are cut before the wheel comes to the drilling

DRILL JIGS

machine. The bottom of rack D has a narrow slot V cut in it
extending from F to G.

A hardened stop-pin E is driven tightly into base B which
protrudes into slot V as shown, thus determining the length
of movement of rack D in each direction. A safety latch H
is fastened to bracket C, swinging about screw / and resting
with its tapered nose upon the taper end T of the low offset

Machinery

Fig. 2. Jig for Drilling Set-screw Holes in Work shown in Fig. 1

portion of rack D. Latch H is held in constant contact with
D by its own weight.

To use the jig drill guides M, bushings R are swung out
and the wheel is slipped upon pin L until the finished rim of
A comes against the finished steel supporting plate K. If
the operator should fail to push the wheel far enough, it will
be impossible to close the drill guides M , as the slot between
the guides that fits over the pinion will only pass over it when
the wheel is in the proper place. Thus the correct location
of the holes is assured. The guides are closed and the first
two holes drilled and tapped. A quick-acting chuck is used to

154

JIG DESIGN

hold the drill and tap. The wheel is now revolved, causing
the rack, the teeth of which mesh with those of the pinion, to
move until the stop-pin E terminates its motion at point G.
The wheel will then have turned 135 degrees and is ready for
the drilling and tapping of the other two holes. After these
are finished, the wheel is turned back until stop-pin E comes
against point F. The operator cannot take the wheel off nor

Machinery

Fig. 3. Jig for Holding Cast-iron Blocks while drilling

put it on until the rack is in the correct starting position, be-
cause safety latch H will be lifted by rack D, thus preventing
the pinion which just passes it when in the lowest position from
being taken off or put on. The operator must, therefore, start
at the proper point for turning the full 135 degrees, and cannot
make the mistake of not turning the wheel back far enough
to achieve that result.

Cam-operated Clamping Slide on Drill Jig. — Two jigs were
required for drilling 50,000 blocks of the size shown at A in
Fig. 3. These blocks were of gray iron, and, when received,

DRILL JIGS 155

were machined all over and accurate within =*= 0.005 inch.
The drilling was performed in two operations; the two J-inch
holes and the }-inch hole were drilled simultaneously in the
first operation, the yVinch h°le being drilled in the second
operation. This order of drilling was necessary, as the f-inch
drills would have been deflected by cutting into the larger hole,
but the iVmch drill having a larger diameter was not affected
by cutting into the smaller holes.

The first problem was to design jigs for holding the blocks
that would require the minimum amount of time in loading
and unloading. At B is shown the jig that was used successfully
for drilling the iVinch hole. It is similar in design and opera-
tion to the one that was used for drilling the two |-inch holes
and the J-inch hole. The jig consists of the cast-iron body C,
which is set on legs five inches high in order to provide hand
room for using the handle D, and also to give a sharper angle
to the discharge chute E, and at the same time to provide
clearance for the receiving box at the end of the chute.

The slide or movable jaw F is made a close sliding fit in the
body C and is held in place by pieces G. Jaw F carries at the
forward end the hardened wearing piece H and the templet
K for guiding the drill, the templet K being attached to the
movable jaw in this case to allow greater freedom in loading.
Sliding jaw F is closed upon the work by the movement of the
cam 7, which is of such shape as to give a powerful grip to the
jaws, a wide loading space, and a quick movement. Tension
spring J holds the slide back, leaving the jaws always in an
open position, except when forced together by means of pres-
sure exerting on the hand-lever D. A carbon steel locating
piece L is doweled to the body to receive the blocks; it is ac-
curately lined up with the hole in templet K. The block when
in place rests on a half floor extending across and in front of
the opening in L. Just in front of this is the large opening into
which the blocks fall, and beneath which the chute E is placed.
A light spring, not shown, knocks the blocks off into the open-
ing when the slide F is withdrawn, and they slide down the chute
into the receiving box. It is only necessary for the operator

156

JIG DESIGN

to place the block in the jig and feed the drill to the work.
Brushes are unnecessary, as the chips clear themselves and
the blocks are freed from chips as they slide over the perforated
section of chute E.

For drilling the three holes in the sides, a multiple drill head
is used and the piece is held in a jig which is a duplicate of the
one shown, except that the templet which guides the drills is

Fig. 4. Jig for Holding Ring while drilling

attached to the stationary jaw and is provided with three holes
for guiding the three drills.

Jig for Drilling Ring. — The jig shown in Fig. 4 at A and B
is used for drilling the ring shown at C. Referring to the illus-
tration at B, it will be seen that there are three plungers D
held against the conical point of wing-screw E by springs F.
In operation, the wing-screw E is turned back until the plungers
D are just within the body G at points H. The ring C is then
slipped on and the wing-screw turned down until the plungers D
are forced out and into contact with the inside surface of the
ring. The ring is then drilled on a sensitive drilling machine.

Indexing Jig operated by Hand-lever and Foot-treadle. —
The drill jig shown in Fig. 5 was designed for drilling four
angular holes in a brass time-fuse cap. (See sectional view of
cap at lower part of illustration.) The principle of this jig can

DRILL JIGS

easily be applied to other work. The jig consists of a hardened
steel locating plate A, mounted on a hardened spindle, which
runs in a bushing that is also hardened. A ball bearing B takes
the thrust of the spindle. At the other end of the spindle is an
index plate C, in which are cut four go-degree notches. Keyed
to the index plate, and also to the spindle, is a ratchet wheel D,

Machinery

Fig. 5. Indexing Fixture operated by Hand-lever and Foot-treadle

having four teeth. A hand-lever E, which has a bearing and
turns around a hub on the index plate, carries a spring pawl F
that engages with the ratchet wheel D. The lever also carries,
at the outer ends, two pins G that project downward, so that
when it is pushed back and forth the pins strike on the body
of the jig and prevent carrying the index plate beyond the
locking pin //. This locking pin is a hardened steel sliding pin,

158

JIG DESIGN

one end of which is rounded and engages with the notches in
the index plate. Back of the pin and held in place by a headless
set-screw K is a coil spring /, which holds the locking pin
against the index plate. The tension of this spring is just
enough to hold the work from turning while being drilled, but
not enough to prevent its being readily indexed by a quick
pull on the indexing lever.

The work is held in position against the locating plate A by
the plunger L, which rests on a single |-inch hardened steel

ft ,. I

Fig. 6. Jig having Lever- and Spring-operated Clamping Members

ball that acts as a bearing while the work is being indexed.
Plunger L is carried in a second plunger M, which is held up
by a powerful coil spring N. This spring should be longer and
stiffer than the one shown, as an enormous pressure can be
obtained with drills as small as the No. 30 used with this work.
The outer plunger M is operated by a foot-treadle connected
to the lever 0. In operation, the foot-treadle is depressed
and a piece of work is placed between the plunger L and the
locating plate A. When the treadle is released, the work is
held by the tension of the spring N while the indexing is done
by the lever E. The locating plate A has slots milled in it

DRILL JIGS

159

with a radius cutter of the same radius as the drill to be used.
This feature, in connection with the lip on the work, answers
the same purpose as a drill bushing, no other means of guiding
the drill being necessary. The production of this jig was about
4000 caps per day.

Jig having Lever- and Spring-operated Clamping Members.

-The jig shown in Fig. 6 is used for drilling i.25o-inch holes

in the motor truck steering arms, shown in Fig. 7. Owing to

the means provided for securing work in this jig ready to be

Machinery

Fig. 7. Type of Steering Arm drilled in Jig shown in Fig. 6

drilled, and for releasing the finished part after the operation
has been performed, this is known as a "pump" jig. Bushing
A is bell-mouthed on the lower side, and drops down over the
top of the boss at the end of the steering arm. The threaded
end of the work is supported by means of a slotted block B
carried at the end of bracket C.

When it is desired to set up a piece of work in the jig,
"pump" handle D is pushed down; this handle swings on
pivots jE, with the result that rods F raise jig bushing A against
the pressure applied by coil springs G. The piece of work is then
slipped into place and handle D is released so that springs G
apply sufficient pressure to enable bushing A to hold the work
in the desired position to be drilled. This arrangement will be

i6o

JIG DESIGN

readily understood by comparing the jig with the work. After
the drilling operation has been completed, it is a simple matter
to release the work from the jig by pushing down the handle D
and withdrawing the piece from under the bell-mouthed bushing.
Drill Jig for Fork Links. —The drill jig shown in Fig. 8 was
designed for drilling fork links. The form of these links is
indicated by dot-and-dash lines in both views. The link has a
round boss at one end and rounded forks at the other end. It

i Machinery

Fig. 8. Drill Jig for Fork Links

is accurately held between two V-blocks, one being adjustable
and the other stationary. The adjustable V-block A is clamped
against the work by the star-wheel and screw shown, and it
travels between finished ways, thus providing an accurate as well
as rapid method of clamping. These V-blocks have inserted
steel plates B and C. The latter, which is in the stationary
V-block, carries a drill bushing for drilling the lower fork, and
an upper shoulder on this plate provides a support for the
upper fork; thus there are two bushings in alignment for drill-
ing the two ends. The inserted plate B in the adjustable block
supports the opposite end of the fork link. With this arrange-

DRILL JIGS

161

ment, a two V-clamping jig is obtained having a three-point
support. This drill jig was accurate, rapid and easily operated.
Drill Jig for Machining Hah* Holes. — A rather unusual
form of jig for drilling a half hole in the work to match a similar
half hole in another piece is shown in Fig. 9. Holes are often
drilled in such locations when it is desired to assemble two pieces
and drive a pin into the hole to act as a driver. To drill such
a half hole, it is usually necessary to plug up the hole in the
work in some way which will back up the side of the drill that
is not cutting. This is accomplished in the present instance

Machinery

Fig. 9. Useful Form of Jig for Drilling Half Holes

by having a stud At which is a push fit in the work, back up
the drill. An angle-iron or plate B is attached to the stud A
and held in position by a bolt C, the plate B being also doweled
in place. A hole is drilled in this angle-iron to receive the
bushing D which guides the drill in the usual manner. The
remainder of the jig consists of the key E which locks the jig
in place on the work.

In using this tool, the key E is pulled back clear of the work
and the stud A which carries the angle-iron is pushed into
the hole until the stud brings up against the shoulder of the
work. By pushing the tapered key E up until it binds on the

162

JIG DESIGN

flat of the work, and then tapping it lightly, the jig is held
securely in place. When drilling one of these half holes it is
found that if an ordinary twist drill is used there is a tendency
for it to "hog in," which is likely to result in breaking the tool.
For this reason, it is desirable to use a straight-fluted or farmer's
drill, although good results may also be obtained by grinding
a twist drill in such a way that it has no rake or hook result-
ing from the spiral form of the flutes. A drill which is ground
in this way presents a square or slightly obtuse cutting edge to
the work, thus doing away with the trouble experienced from
drills breaking when ground in the usual way.

Machinery

Fig. 10. Drill Jig provided with Rockers to Facilitate
Reversing its Position

When drilling the hole, the work is set up on end on the drill
press table and the drill is fed through the bushing in the usual
way, the bushing holding the drill in position until it starts to
cut. As the drill is fed down, there is a tendency to force it
away from the work, but this tendency is resisted by the
hardened stud A so that the half hole is drilled parallel with
the axis of the work. This jig affords a convenient means of
quickly accomplishing this work and having the two half holes
match up accurately, so that no difficulty is experienced in as-
sembling the work.

Jig having Rockers upon which it is turned over. — The box
drill jig shown in Fig. 10 was used for drilling three holes in a
certain piece that was to be produced in quantity. The jig is

DRILL JIGS

made from a forging, two stationary bushings being inserted in
the top and one in the bottom. As the jig and work weighed
about twelve pounds, it was hard for the workmen to be con-
stantly lifting the jig and turning it over for the operation on
the other side; therefore, two pieces of steel were machined to
a radius and attached to the jig between the four feet on the
side opposite the leaf. With the aid of these rockers, the jig
is easily turned over from one side to the other. They do not
interfere in any way with the working parts, and when changing

Fig. 11. Drill Jig designed for Rapid Indexing

work, the jig is supported by the rockers. In this way, the jig
is always on the drilling table, and there is less likelihood of
the operator letting it fall to the ground or throwing it down
and snapping the bushing or legs, which are hardened to glass
hardness. In addition, the operator does not have to work so
hard and the production is considerably increased.

Drill Jig designed for Rapid Indexing. — The necessity for
a drill jig of the indexing type was brought about by a certain
design of motorcycle drive pulley. This pulley is of the flat-
belt, flanged type, having cork inserts over its entire periphery.

164 JIG DESIGN

To the right in Fig. n is shown a completed pulley with the
cork inserts in place. Mounted on the drill jig is shown a pulley
being drilled. The pulley is 4^ inches in diameter and has 42
holes, | inch deep, arranged in three rows of 14 equally spaced
around the periphery. The drill jig is built in such a manner
that it will take a large variety of sizes of pulleys.

At the left of the jig is shown a large drum which serves as
a means of indexing the drill jig readily, and has three annular
grooves on its periphery, spaced the same distance apart longi-
tudinally as it is desired to have the holes drilled on the pulleys.
Directly in the center of these grooves and spaced equidistantly
around the periphery are 14 tapered index pin holes. At the
base of the drill jig is an index pin (not shown), which is tapered
on the end to fit the tapered index hole. At the back of this
index pin is a light spring which holds it constantly in contact
with the index drum.

In operation, the first row of holes is drilled. When enough
pressure is applied to the drum to rotate it, the index pin,
being correctly tapered, will jump out and allow the drum to
revolve to the next index hole. After the first row of holes has
been drilled in this manner, the second row is placed in line
with the revolving drill by forcibly sliding the index drum and
its shaft longitudinally until the index pin jumps into the mid-
dle groove. In this position the 14 central holes are drilled as
before. To drill the last row of holes it is only necessary to
move the index drum over as in the second case.

Where it is essential to drill holes accurately spaced around
the periphery, this form of index drum and pin might not be
accurate enough. However, in this case and in many other
cases it is sufficiently accurate. It has the advantage of being
quickly indexed, which is not always true of the ordinary index
pin that has to be grasped by one hand while the other hand is
employed in rotating the fixture. In this case, the right hand
is never moved from the drill spindle lever.

Indexing Jig provided with Work-locating Device. — The
jig shown in Fig. 12 is for drilling differential spider arms.
Before the drilling operation the forging is chucked and rough-

DRILL JIGS 165

turned, including the arms, and then without centering the ends
of the arms the piece is casehardened. A row of hardened
spiders is then strung on an arbor and sufficient metal is ground
from the ends of the arms to remove the hardened case. This
leaves the soft cores exposed for center drilling. By drilling

Fig. 12. Indexing Jig provided with Special Work-locating Device

after hardening, a better working center is obtained, and one
that is not full of scale; moreover the centers are not influenced
by any distortion that might occur in hardening.

The jig upon which the center drilling is done consists of the
angle-iron base A, upon which is swiveled the jig section B.
The spider, which is indicated at C, is slipped over the swiveling

i66

JIG DESIGN

stud D. In order to locate the spider centrally in the jig, that
is, so that the arms will come in average alignment with the
four bushings, the centering device E is employed. By means
of a spring F, the end of which is attached to the bent end of
the part E, the two aligning fingers are brought to bear simul-

Fig. 13. Trunnion Type of Indexing Jig for Automobile
Rear-axle Housings

taneously against opposite arms of the spider, thus locating
the spider in a central position in the jig. After this it is a
simple matter to drill and countersink the spider arms one
after another, indexing the jig by hand for each arm.

An idea of the facility with which this jig is operated can be
gathered from the fact that 500 of these spiders are drilled

DRILL JIGS '167

and countersunk in a day of nine hours, making a total of 2000
holes per day. The most important part, however, is the fact
that the method insures that the centering is done with refer-
ence to the hardened spider arms, thus insuring that the amount
of metal removed in grinding will be practically equal at all
points.

Indexing Jigs mounted on Trunnions. — A box drill jig for
use in drilling, reaming, tapping, chamfering, and spot-facing
holes in automobile rear-axle housings is illustrated in Fig. 13.

Fig. 14. Another Indexing Drill Jig of the Trunnion Type

It will be seen from the illustration that the jig swings on trun-
nions fitted in the cradle or base, and that the base is equipped
with index-pins for locating the jig in any of five positions.
There is an index-pin at each side of the base and these pins
are operated simultaneously by a single hand-lever.

The rear-axle housing is put in the jig through an opening
covered by a hinged and latched lid; and the work is held in
place by means of hardened steel plugs which insure positive
location. All parts of the jig which are subject to wear are
hardened and ground to size, thus greatly reducing the possi-
bility of inaccuracy of the work as a result of wear. The weight
of the jig is noo pounds and it is equipped with rollers carried
» J

i68

JIG DESIGN

by hardened and ground steel pins. These rollers run on tracks
which carry the jig under the machine and also enable it to be
easily run back to remove the work.

It is necessary to drill quite a number of holes in the casting
shown in place in the jig illustrated in Fig. 14, and these holes

Machinery

Fig. 15. Multiple Drill Jig for Yoke Ends

are located on different sides and at various angles to one
another. For this reason, an indexing jig is employed. This
particular illustration shows the cover A of the jig removed
in order to illustrate more clearly the position of the casting,
which is located in the jig by its trunnions. The main body of

DRILL JIGS 169

the jig is also supported by heavy trunnions at each end,
and the large disks B and C enable it to be held in different
positions. These disks contain holes which are engaged by
suitable indexing plungers D at each end of the fixture.

Multiple Drill Jig for Yoke Ends. — In automobile shops,
the part shown at X in Fig. 15 is known as an adjustable yoke
end. Even the simplest motor car employs many such parts,
and it will therefore be understood that jigs for drilling these
yoke ends must be designed with a view to high production.
The jig used for drilling the hole H in six yoke ends at the same
time by means of a multiple-spindle drill head is rather com-
plicated in detail, but may be operated very rapidly.

It is required that the hole H be practically concentric with
the round end, so that the piece is located in a V-block, between
the two pins Y, shown in the upper view where the plate is
broken away. The locating is accomplished by pushing the
yoke end between the V-blocks V and the flat steel springs 5.
The bushing plate T and the entire clamping assembly is re-
moved at this time to make the jig accessible. After the parts
have been placed in position in the jig, the bushing plate and
assembly are put back in place, and as the pin C enters the
slot, it is pushed down to the bottom of the socket K and
locked by turning the knob M clockwise. The bushing plate
is brought to the right position by registering with the pin E,
which location also brings the lower buttons of the equalizer
bars B directly over the yoke ends. Turning the nut L clock-
wise by means of the removable handle F brings it against
the spherical seat of the clamp plate N which, in turn, com-
presses the helical spring G and brings the equalizer bars
against the work. The handle F is then removed and the work
drilled. Reversing the process and rapping the baseplate D
against the drill table releases the work. The function of the
helical spring G is to keep the plate N against the nut L so
that a small movement of the handle F will permit of unclamp-
ing the plate. A hardened steel plate A is provided for a seat
on which the work rests. It should be noted that the slot in
the yoke end is milled out in an operation following the drilling.

170

JIG DESIGN

A Vise Drilling Jig. — Fig. 16 shows a jig for drilling and
milling an elongated hole in a piece of work where the limit of
accuracy required is not less than =*= 0.003 mcn- A flanged
milling machine vise was fitted with a special jaw having a
V-groove cut lengthwise, as shown at B. Pin C was put into

Machinery

Fig. 16. Vise Drill Jig with Swiveling Leaf for Forming an Oblong Hole

a soft jaw on the movable slide of the vise and located so that
the milled surface of shaft A would rest on the upper surface
of the pin and hold the shaft level for drilling. Bushing plate
D was next put on and held in place by a cap-screw E. Bushing
plate D was then laid out and drilled and reamed in position
for the locating pin F and the drill and counterbore bushings G.
The stop-pin H was located in the bushing plate D to insure

DRILL JIGS 171

obtaining the right location of the drilled hole from the end of
the shaft A.

After the hole was drilled, the locating pin F was pulled out
and the plate D swung around from the first position, as shown
by the dotted lines, to the second position, and pin F was in-
serted in another hole. Each hole for pin F was located so as
to bring the bushing plate D into the proper positions for drill-
ing and counterboring. A special counterbore or mill was then
used through the bushing G to elongate the hole to the proper
size and depth. This counterbore was made from drill rod of
the same diameter as the width of the elongated slot in the
shaft. Four teeth were cut in the end and it was then hardened
and tempered.

After the shaft A was properly drilled and counterbored, it
was removed from the vise, and the bushing plate D swung
back into the drilling position; this also brings the stop-pin
H into position for locating the next shaft. Another shaft is
now put into the vise against the stop-pin and the previous
operations are repeated.

This device has been used with new bushing plates to suit
many different kinds of work. For drilling and tapping, when
using a reversible tapping chuck or a drill press that has a
reversible spindle, it will be found to be a very handy tool.
After the tap hole is drilled in the work, pin F is pulled out
and bushing plate D can be swung out of the way.

Jig for Drilling Deep Holes in Studs. — The jig to be de-
scribed was designed for drilling 50,000 brass studs which were
turned from a |-inch square bar, with a short section of the
original square bar left at the center of the finished stud. The
drilling operation could not be done conveniently on the auto-
matic screw machine, as it was necessary to drill a ^-inch hole
to a depth of 2\ inches.

The machine used is a speed lathe which is provided with
both wheel and lever feed for the tailstock. For this work,
the tailstock spindle was removed and replaced by a special
spindle which is shown at A in the cross-sectional view, Fig. 17.
In the illustration it will be seen that the spindle is provided

172

JIG DESIGN

with a threaded nose on which the bracket B is screwed.
The spindle was bored out to such a size that the work-holder
C is a sliding fit in the spindle, the movement of the work-
holder being accomplished by means of the lever D which is
pivoted to the bracket B. The quadrant E is provided with
teeth for the purpose of locking the lever in the closed position.
One of the studs to be drilled is shown in position at F in
the work-holder. It is accurately centered between the tapered
drill bushing G at one end of the work-holder and the tapered
end of the rod H at the opposite end of the holder. The drill

ORILL-^-INCH HOL
2% INCHES DEEP

Machinery

Fig. 17. Jig for Drilling Deep Holes in Studs

bushing is pressed into the end of the work-holder, and the
design of the work-holder and the manner in which the rod H
is threaded into the. tailstock screw are all clearly shown. In
setting up a piece of work in the jig, the rod H is held stationary
by its threaded connection with the tailstock screw, and a
movement of the lever D releases or re-centers the work by
sliding the work-holder C in the spindle A, the work-holder
being prevented from turning by means of a clamp J which
engages the square which is left at the center of the stud.

The drills used for this operation were of exceptional length
and made with an increase in the angle of twist. They were
held in the lathe spindle and the work was fed up to the drill
by means of the tailstock lever. The use of this lever feed
made possible the quick return of the work, which enabled

DRILL JIGS

173

the work to be rapidly backed off. This was an advantage as
it was necessary to back off the work several times in drilling
each hole in order to clear the chips from the drill to prevent
breakage. The average rate of production obtained with this
fixture was one piece per minute, the time required for setting
the work up in the fixture being not over three seconds.

Machinery

Fig. 18. (A) Jig in Position for Drilling Straight Hole. (E) Jig in
Position for Drilling Angular Hole

Jig for Straight and Angular Drilling. — The jig shown in
Fig. 1 8 was designed for drilling two holes, one of which was
on an angle. By the use of this jig, the operator can bring the
jig quickly into the correct position for drilling the two holes.
When drilling the straight hole, the jig is in the position shown
at A; when the operator desires to drill the angular hole, he
simply lifts the front of the jig, and the swinging leg C falls,
bringing the jig into the position shown at B, and placing the
hole to be drilled in a line with the drill. By using this jig,
extra parts, such as a cradle or angle-block, are eliminated.

Quick-operating Drill Jig. — The design of quick-operating
drill jigs is a difficult matter, particularly when the shape of

DRILL JIGS 175

the work is such that it must be located in more than one direc-
tion and clamped at several points. If the necessary clamps
could be positively operated by a single lever, the greatest
possible speed would be obtained, but this ideal condition may
not be practicable, owing to the fact that the holding position
of each clamp is likely to vary with the size of the work, thus
making any combined positive movement of the clamps inef-
fectual. The clamps may be released by a single lever, but when
holding the work their position is fixed by the work itself, and
this condition, coupled with variations in the size of the work,

°]

Machinery

Fig. 20. Work to be drilled in Jig shown in Fig. 19

makes the operation of the clamps by a single lever a difficult
matter.

If it were always possible to reverse this condition, making
each clamp independent of the others in its closing movement
and thus compensating for varying sizes of work, a single lever
might be arranged to release all the clamps at once. This de-
sirable result has been accomplished in the jig shown in Fig. 19
by employing spring pressure to close the locating and holding
mechanisms. The position of the work is fixed in two direc-
tions, and the work is clamped at two points by a single move-
ment of the operating lever to the right, while moving this lever
to the left releases the work from the clamping and locating
devices. The work (which is shown on a reduced scale in Fig.
20) lies on three hardened steel blocks A, and is located be-
hind pins B mounted in these blocks and to the left of the pin
C in the base of the jig.

The block D forms a seat for the cover-plate and the latch
which holds the cover-plate down is pivoted in this block. The
latch is held down by a spring plunger. The bellcrank lever E,

176 JIG DESIGN

which carries the fourth locating pin, is pivoted to the base
of the fixture and provided with a lug which enters an opening
through the base and receives the pressure of the spring
plunger F. The brackets G are attached to the base of the
fixture and the cover-plate is hinged to these brackets. The
brackets are also bored out to receive two spring plungers.
The operating lever is fastened to a hub H and a link / is
pivoted on this hub, the opposite end of the link being attached
to the hub J. The screws which hold the operating lever to
the hub H, and the link / to the hub 7, are extended to form
pins which engage the levers K.

The jig is shown closed with all parts in the positions they
would occupy when holding a piece of work. To raise the
cover-plate, the latch is pressed back, when the thrust of a
spring plunger raises it sufficiently to prevent the latch re-
engaging the cover-plate. The cover-plate is raised to the
limit of its movement which is a few degrees beyond the per-
pendicular. The operating lever is then swung to the left until
it strikes a limit pin. This movement of the lever turns the
hubs H and /, bringing the pins against the tail ends of the
levers K and compressing the springs behind the plungers carried
in the brackets G. Thus, the ends of the levers K which
engage the work are swung back, releasing their grip.

The final movement of the left-hand lever K brings the ad-
justable stop- screw L carried by this lever against a lug pro-
jecting above the lever E, thus compressing the spring F
and releasing the work from the pressure of the pin carried
by the lever E. The screw L limits the movement of the lever
E to the minimum amount necessary to release the work, and
the stop-screw may be adjusted to accomplish this after the
jig has been locked open. After removing the work from the
jig, an undrilled piece is placed in position and the operating
lever thrown to the right. This causes the different holding
members to go through their sequence of movements in the
opposite order to that described for releasing the work from
the jig. The result is that the work is clamped in place in a
minimum amount of time.

DRILL JIGS 177

Drill Jig equipped with Milling Attachment. — The drill
jig shown in Fig. 21 has mounted upon it a straddle-milling
attachment for straddle-milling two bosses and cutting two
oil slinger grooves in the lower half of an automobile crankcase.
The crankcase is rigidly held in adequate supports in the drill
jig, so that the light milling operation can be conveniently per-
formed at the same time. The use of the jig for milling is also
desirable, because the bosses must be in an accurate position
in relation to the drilled holes.

Fig. 21. Trunnion Type of Drill Jig equipped with Milling Attachment

In Fig. 21 the drill jig is shown in the loading position. The
jig templet plate A has to be removed when the crankcase is
being loaded on the jig. The crankcase is located by setting
the outline to permanently located lines on the face of the jig.
When the correct position is obtained, the crankcase is firmly
clamped by four straps. After the crankcase is clamped into
position, the templet jig A is replaced, being held down by the
hand-nut B and located by a keyway in its under surface and
a key in the main body of the drill jig. While in the position
shown, the holes are drilled and tapped through the templet
jig A, and this jig is allowed to remain in place, acting as a
clamp, while the drilling and milling are being done.

After the completion of the foregoing operation, the drill

1 78 JIG DESIGN

jig is indexed to the position shown in Fig. 22. While in this
position, 22 holes are drilled in the crankcase, and after these
are completed the milling is done. The milling attachment
for this drill jig consists of two members D and C. Part C
consists of a body member for the milling attachment. In this
member are cut vertical ways in which the cutter carrying
member D travels up and down. The movable member D
carries a horizontal cutter-arbor having a gang of three cutters /
and G on each end. In the center of this arbor is a bevel gear
which meshes with another bevel gear carried by a vertical

Fig. 22. Jig in Position for Drilling and Milling Operations

shaft, the upper end of which terminates in a Morse taper
shank E. The movable member D is held normally in the upper
position by springs.

In operation, the drill spindle is brought down in contact
with the taper shank E until it is seated into the taper drill
socket. Then the drill spindle is rotated, and the milling arbor,
of course, rotates also through the bevel gears. The drill
spindle is fed downward the same as for drilling, and in so
doing the entire member D is lowered until the right-hand set
of cutters G is brought into contact with the boss to be milled
at the right-hand side of the crankcase. The cutters continue
to be lowered until they come against a previously set stop, in
which position the milling of the right-hand boss is completed.

DRILL JIGS 179

To proceed with the milling of the left-hand boss, it is neces-
sary to loosen the straps that hold the milling fixture in place,
grasp the handles H and lift the milling attachment over to
the left-hand side of the drill jig, where there are dowel-pins
which accurately locate it in its correct relative position. The
operation is repeated in the same way as for the right-hand
boss, except that cutters / are used instead of cutters G. This
milling attachment is never removed from the drill jig, except
as explained, for milling the right- and left-hand bosses. The
movable member D is moved up out of the way by spring pres-
sure when a new crankcase is being placed in the jig. It would
be possible, of course, to equip this drill jig with two milling
attachments, one at each end, so that it would not be necessary
to move the attachment from one side to the other, but as the
changing of the fixture from one side to another was such a
simple matter, it was not deemed advisable to go to the extra
expense that this would involve.

Jig for Cross-drilling Pistons. — The jig shown in Fig. 23
is used successfully in cross-drilling pistons. The piston is
drilled from both sides and not all the way through from one
side, which is the common practice, especially when the work
is done on some kind of lathe. It is not an easy matter to drill
and ream a true hole by starting on one side of the piston,
drilling through one boss, and then advancing the tool across
the opening between the bosses and expecting the tool to secure
a true start in the second boss.

This jig was made in the following manner to insure accuracy.
A block of cast iron was milled square and the large hole rough-
bored to within TV inch of size. This block was then milled
across one end to receive the stop-bar A. After fitting the
stop-bar, it was removed and the seat for the clamp-bar B
was bored by using a fly-cutter in the milling machine. This
clamp-bar was a piece of two-inch cold-rolled stock, milled
flat to form a little more than a half round. During the suc-
ceeding boring and grinding operations the clamp-bar was held
to its seat by the two screws C which had washers under their
heads instead of the springs shown in the illustration. A piece

i8o

JIG DESIGN

of o.oo5-inch stock was placed between the clamp-bar and
seat while boring and grinding; this shim was taken out later
to allow for a little clearance. After the clamp-bar was fitted
and bored, the holes for the hardened bushings D were bored
and the bushings fitted. These bushings were long enough to
reach through the large bore so that they could be ground flush
with the inside of the jig.

The jig was next set up on the table of a Heald cylinder
grinder and the holes in the bushings ground in line and true

Fig. 23. Jig used for Cross-drilling Pistons

to size. The jig was then placed on one side with the bush-
ings in a horizontal plane and the large hole finished to size
by grinding. To be sure that the holes in the bushings would
be perfectly central with the large bore, an arbor was ground
to a snug fit for the bushings and the large hole was gaged
from it, measuring from the wall of the large hole to the arbor
until both sides were exactly the same. The hole was then
finished 0.003 mc^ larger than the piston to be worked on.
Two slip bushings E were made to fit the bushings in the jig,

DRILL JIGS l8l

one for the three-lipped drill and the other for the reamer.
The reamer used was 0.0015 inch under size, so that the holes
could be finished with a long hand reamer that reached through
both holes of the piston.

To locate the piston in the jig so that the bosses would line
up with the holes being drilled, the "locator" shown at the
open end of the piston was made and used in the following
manner. The locator consists of the cross-bar F, into which
are fitted the knob G that is used for a handle, two flat bars H
with V-slots in the ends, and the two pilot-pins /. The pilot-
pins fit into holes /, bored in the face of the jig in line with the
bushings. In using this locator the piston was first put into
the jig and then the locator was pushed in until the V-slots
came in contact with the bosses. This put the piston in such
a position that the bosses were in line with the drill bushings.
After locating, the piston was gripped by the clamp-bar by
tightening the set-screw K.

In this case the pistons were rough-drilled •/% inch under
size before turning, so that in this jig it was only necessary
to use one drill and reamer. The drilling operations were as
follows: The drill bushing was put in and the drill run through
one side. The bushing was then taken out, the jig turned over,
and the bushing put in the other side, after which the second
boss was drilled. The drill bushing was now replaced by the
reamer bushing and the hole reamed; the bushing was then
taken out, the jig turned over, the bushing replaced and the
second hole reamed. When using this jig two strips were fas-
tened to the drill press table forming a channel in which the
jig could slide and which would also hold the jig in line with the
machine spindle.

Jig for Facing Bosses in Pistons. — Fig. 24 shows the jig
and facing bar used for facing the bosses in the piston after
it leaves the cross-drilling jig. It was found advantageous to
do this operation in a separate jig because it consisted of top
and bottom facing and also because the machine spindle had
to be set to a stop. This jig proved to be a very handy and
rapid tool. The base and the adjustable top are provided with

182

JIG DESIGN

a pair of jaws bored to the proper size to fit the piston to be
worked on. The springs on the upright studs hold up the upper
or clamping jaw while the work is being put in or taken out.

In operation, a piston is slipped between the jaws, the facing
bar run down through the cross-drilled holes, the cutter fitted
into the bar, and the top jaw set by a half turn of the lever-
handled nut. A feature of the facing bar is the manner in

Machinery

Fig. 24. Jig used for Facing the Piston Bosses

which the cutter is held. It will be seen that the cutter has a
half-round notch in the center of the bottom edge that registers
with a steel ball L in the center of the cutter slot. A stiff spring
holds the ball to its seat in the bar. The cutter is also provided
with two holes near each end that are used for pulling it out
of the bar with a stout wire hook. It is double edged, so that
both bosses can be faced without reversing it or stopping the
machine. This method of holding the cutter would not be
desirable in the case of a boring tool, but for a facing tool it
serves very well. Of course the cutter must be a nice fit in the

DRILL JIGS

183

bar. When the facing jig is used it can be clamped to the
machine table, while the cross-drilling jig is not clamped, be-
cause it is necessary to turn it over and over.

Universal Jigs. — While a large percentage of the jigs in
common use are designed especially for some part and are used
exclusively for that particular part, occasionally jigs are so
constructed that they are adjustable and adapted for a variety
of work. For this reason they are often called " universal"
jigs. Jigs of this type may resemble an ordinary jig somewhat

Fig. 25. Toolmakers' Universal Drill Jig

and simply be arranged to locate the guide bushings (in the
case of a drill jig) in different positions; or the jig may be in
the form of a special attachment for the drilling machine.

An example of universal jig construction is shown in Fig. 25.
This is a very simple design and consists of a plate containing
one or more drill bushings and adjustable locating rods. It
may be used for accurately locating and drilling holes in jigs,
dies, and templets. A hardened and ground block A is pro-
vided with four sliding pins B, a set of removable bushings C,
and eight headless set-screws. Bushings C may be made up
with various sized holes to provide for guiding different sizes of
drills. Small slugs of brass or copper are used between the set-
screws and the pins B so that adjusting the screws will not
tend to change the position of the pins.

12 J

1 84

JIG DESIGN

To illustrate the use of this jig, suppose that a number of
holes must be accurately located, drilled, and reamed in a die-
block. After the block has been planed up perfectly square,
parallels are clamped to the edges so that they overhang in
the manner shown in Fig. 26, allowing the pins B to engage
with these parallels when the jig is laid flat against the die-
block. The bushing C is located at a known distance from the
edges of the jig, and by setting the pins B in the required
position by means of a micrometer or micrometer depth gage,

Machinery

Fig. 26. Method of using Universal Drill Jig shown in Fig. 25

the bushing is located in position for drilling the hole in the die-
block. For this purpose, the jig is clamped to the die-block with
a pair of parallel clamps, after which the hole is spotted, drilled
and reamed in the usual way. It will, of course, be evident
that any number of holes that come within the range of the jig
can be located on the die-block in the same way. The useful-
ness of this tool will be apparent to any toolmaker, and many
uses will be found for it that may not be seen at the first glance.
A universal jig which is in the form of an attachment which
is clamped to the table of a drilling machine is shown in Fig. 27.
The drill bushing is in line with the axis of the machine spindle,
so that holes may be drilled as in the case of an ordinary jig,
and there is a compound table with slides at right angles, which

DRILL JIGS

are operated by the usual screw and ball-crank combination.
These screws are merely employed for making approximate set-
tings; the actual locations which are depended upon to secure
accurate spacing of the holes are made by means of microme-
ter heads and standard distance bars. The work-table is
adjusted until both micrometers read zero against stops
on the table which act as the micrometer anvils, and in this

Fig. 27. Universal Jig which is in the Form of an Attachment for Drilling Machine

position the center of the drill bushing is located over the inter-
section of the guide strips on the work-table. The work is
clamped against these guides, and in starting to locate the first
hole, the two table slides are manipulated so that an approximate
setting is secured, after which the distance bars and micrometer
heads are used to obtain the final location in the manner to
which reference has already been made. The arm which sup-
ports the drill bushing should be set to bring the bushing as
close to the work as possible. It is possible to use this equip-

i86

JIG DESIGN

ment to locate any number of holes in the work in the desired
relation to each other, as the table slides may be manipulated
and final settings made with the micrometer heads and dis-
tance bars, so that each hole is located in the proper relation
to the preceding hole. Clamps are provided to lock the table
in each position before the drilling operation is started.

The distance bars are supported by bushings held in
V-shaped seats, which support them at the proper height to
line up properly between the micrometer spindles and stops on
the table which come in contact with the micrometer spindles

Fig. 28. Vise with Jig Attachment

when the table is set in the zero position. Johansson or other
gages may be used in place of the distance bars, if so desired.

Jig Attachments for Drilling in Vises. — The machine vises
such as are used for milling or planing operations may be used
for drilling when they are provided with attachments for hold-
ing drill bushings or locating stops. There are now on the
market vises furnished with jig attachments ready for use.
One of these vises is illustrated in Fig. 28, where it will be seen
that a stop A may be used to locate the work while the bracket
B holds the bushing which guides the drill.

As a simple illustration of the principle involved in using
a jig of this type, reference is made to Fig. 29, in which the
part being machined is a round collar. This collar A is gripped
against a vee in the solid jaw, and the bracket containing the

DRILL JIGS

i87

Machinery

Fig. 29. Vise equipped with Jig Attachment and V-blocks for Gripping
Cylindrical Part

I yy v-/ " h

-1— M 1 I, ,-il !l II ll

u u

^=n

'Machinery

Fig. 30. Drilling Several Holes with a Templet attached to Vise

1 88 JIG DESIGN

bushing B is adjusted to tlie correct position for guiding the
drill into the work. It is clamped in place on the solid jaw by
means of bolts C. To operate the jig, the movable jaw is
opened and a piece of work inserted in the V-block; then it is
only necessary to tighten the jaws and proceed to drill. In this
way, duplicate parts are obtained without an elaborate jig.
By using suitable plates in these jigs, many odd-shaped pieces
can be drilled, of which Fig. 30 is a typical example. The method
of using this plate is shown by the illustration. Bushings A are
placed in the plate B at the proper location to guide the drills
into the work. The plate is screwed on top' of the vise, the stop
C is adjusted to the proper location, and the work D placed in
the vise against the stop, after which the holes are drilled.

This jig construction adapted to drilling holes on an angle
is illustrated in Fig. 31. In this case, a swivel vise is fitted
with a plate A set at the proper angle in relation to the base B.
Then by swinging the vise up to the proper angle, the parts
may be drilled in duplicate as in the previous case cited. That
there are infinite possibilities in the fitting of vises with bush-
ing plates, when these are intelligently used, will be readily
seen by considering the methods of drilling illustrated in Fig. 32.
This illustrates a swivel vise used as an indexing jig, and where
extreme speed or accuracy is not required it works out very
satisfactorily. The first drilling is done with the vise in the
position illustrated. The subsequent drilling is accomplished
by tilting the swivel vise to the right and left the desired number
of degrees.

Another example of drilling in a vise is shown in Fig. 33,
a number of holes being drilled around a circle. The work
is gripped between the jaws in the vise proper and a bushing
plate is located by pins A and B in the vise. By sliding the vise
to various positions the holes are drilled in the usual manner.
This bushing plate is removable for taking out the work.

The vises here illustrated are not always the most economical
means of handling work, but they are often the best that the
extent of the job will warrant. They must not be confused
with more elaborate jigs and fixtures which, although vises

DRILL JIGS

189

Fig. 31. Vise provided with Drilling Attachment — Set for
Drilling at an Angle

Machinery

Fig. 32. Swivel Vise equipped with Bushing Plate and arranged for
Angular Drilling

1 9o

JIG DESIGN

in principle, are special in construction. Not all shops can
afford the costly design that the manufacture of guns or auto-
mobiles will warrant. They must compromise on the cheaper
and less effective equipment that can be adapted quickly to a
wide range of work, and the machine vise, as shown in the
foregoing, can be made a universal fixture within its limits.

Multiple Drilling Jig of Reversible Type. — The drilling of
the spoke holes in the hubs of motorcycles is illustrated in Fig. 34.

Machinery

Fig. 33. Vise provided with Removable Bushing Plate for Drilling
Holes on a Circle

These hubs are made of low carbon steel and the end flanges
through which the holes are drilled are J inch thick. Through
each flange, sixteen No. 25 holes are drilled at a slight angle
so that the direction of the drilling is along the lines of a cone.
The distance between the holes is about one-half inch.

The spindles of the multiple-spindle drilling machine in
which the work is done are guided in their inclination by a
steel ring supported from the head of the machine. The jig
is of the swiveling type, permitting the holes in one end of
the hub to be drilled, after which the work-holding part of

DRILL JIGS

Fig. 34. Swiveling Drill Jig for Motorcycle Hubs

the jig is swiveled 180 degrees and the holes in the opposite
end are drilled. The drilling is performed by running the head
and drills down to the work, which on account of the inclina-
tion of the spindles is the only way possible.

IQ2

JIG DESIGN

In order that the work may be quickly inserted and removed,
the jig is made in halves. As the illustration shows, these
halves are hinged at the left and held together for the drilling
by a latch that appears at the right of the illustration. The
drill bushings are located in the faces of the halves of the jig.
After the holes in one flange of the hub have been drilled,
the steel plate that takes the thrust is removed from beneath

Machinery

Fig. 35. Jig for Drilling Holes in Power Press Dial Plates

the work. Then by withdrawing the index-pin at the left, the
working part of the jig can be turned 180 degrees to present
the other face of the hub to the drills. The heavy stud on
which the jig swivels is directly behind the work, and, there-
fore, not visible in the illustration. The index-pin is inserted,
the thrust plate is replaced, and the drilling of the hub is com-
pleted. The hubs, each having 32 holes — 16 in each end —
are drilled at the rate of 300 per ten-hour day.

DRILL JIGS

193

Jig for Drilling Power Press Dial Plates. -- The jig shown in
Fig. 35 is used for drilling dial plates of the form employed on
automatic feed mechanisms for power presses. These dial
plates have the center hole bored and the notches milled to
suit the locating plungers on the power presses, but the holes
had to be drilled later because they are located with reference
to the particular presses on which the dials are used. Before

Machinery

Fig. 36. Jig in which a Single Screw tightens both Clamp and
Hinged Cover

using the drill jig it was necessary to make center punches to
fit the punch-blocks on the different power presses and also to
fit bushing A in the jig. Each dial plate B was then put on its
bed and the press was set in the usual way, care being taken
to have the locking device fit properly in one of the notches.
The center punch was then mounted in the punch-block and
one prick-punch mark was made on the dial in the proper
relation to one of the notches. The dial plate was next placed

1 94 JIG DESIGN

on the table of a drill press and the center punch was set in
the chuck in the drill spindle so that the prick-punch mark on
the dial could be lined up with the spindle. The plate was then
strapped to the table and stud C driven into the center hole.
The top of the stud C is machined to fit the pivot hole in the
arm D of the jig.

The next step consisted of lining up the bushing A of the
fixture with the center punch in the drill spindle. It will be
noted that the bushing is made adjustable relative to the center
C about which the arm swings, so that it may be set in the
required position before clamping the binding bolt. The bush-
ing is located in the proper relation to the notches in the dial
plate by means of the locking pawl E, and the eccentric screw F
adjusts the position of the pawl relative to the arm D of the
jig. The pawl is held in the proper notch in the dial by the
spring G which is mounted on the pins H and /; and stud / is
used to hold the arm of the fixture true with the face of the dial
plate. It will be evident that after this setting has been made,
the bushing A is located directly over the center punch mark
which was made on the dial plate while the prick-punch was
mounted in the punch-block of the power press. The hole can
now be drilled in the dial plate, after which successive holes
are drilled by simply swinging the dial around the pivot C
and locking it for drilling each hole by dropping the pawl E
into successive notches in the dial plate.

Duplex Clamping Arrangement on Drill Jig. — The jig shown
in Fig. 36 is used for drilling and tapping stud A, which is
made from J- by J-inch cold-drawn steel. The end of the stud
enters hole B in the locating block, and this hole is milled to
provide clearance for the head of the stud. The work rests on
the drill bushing which is slightly counterbored to provide clear-
ance for the tap. The most interesting feature of the jig is that
the cover and clamping mechanism are both secured by the same
knob; clamp C holds the stud securely in place when the knob
is screwed down, and the same operation tightens the cover. It
will be readily seen that this principle could be employed on
jigs and fixtures used for holding a great variety of parts.

CHAPTER VIII
BORING JIGS

Boring jigs are generally used for machining holes where
accuracy of alignment and size are particularly essential, and
also for holes of large sizes where drilling would be out of the
question. Two or more holes in the same line are also, as a
rule, finished with the aid of boring jigs. The boring operation
is performed by boring bars having inserted cutters of various
kinds, and boring jigs are almost always used in connection
with this kind of boring tool, although boring operations may
be satisfactorily accomplished with three- or four-lipped drills
and reamers. The reamers may be made solid, although most
frequently shell reamers mounted on a bar and guided by bush-
ings are used. The majority of holes produced in boring jigs,
whether drilled or bored out, are required to be of such accuracy
that they are reamed out in the last operation.

The boring-bars are usually guided by two bushings, one on
each side of the bored hole, and located as close as possible to
each end of the hole being bored. The bar is rotated and
simultaneously fed through the work, or the work with its jig
is fed over the rotating bar: Boring jigs may be used either
in regular boring lathes, in horizontal boring and drilling
machines, or in radial drills.

The jig body is made either in one solid piece or composed
of several members, the same as in drill jigs. The strain on
boring jigs is usually heavy, which necessitates a very rigidly
designed body with ribbed and braced walls and members, so
as to allow the least possible spring. As boring jigs when in
operation must be securely fastened to the machine table,
means must also be provided in convenient and accessible
places for clamping the jig without appreciably springing it.

195

196

JIG DESIGN

The places in the jig where the bushings are located should
be provided with plenty of metal so as to give the bushings a
substantial bearing in the jig body. Smaller jigs should be
provided with a tongue or lip on the surface which is clamped
to the machine table; this permits the operator to quickly
locate the jig in the right position. As an alternative, finished
lugs locating against a parallel or square may be provided.
It is frequently advantageous to have small sized boring jigs
provided with feet so that they can be used on a regular drill-

— | r-

'•

J |

1 !

! !

Fig. 1. General Outline of Simple Boring Jig

press table in cases where holes to be bored out are to be opened
up with a drill piercing the solid metal. It is both easier and
cheaper to do this rough drilling in a drill press.

The guide bushings, of the same type as the bushings for
drill jigs, are made either of cast iron or steel and ground to
fit the boring-bar, which is also ground. The bushings should
be made rather long to insure good bearing.

Boring Jig of Simple Design. — The most common type of
boring jig for small and medium size work is shown in Fig. i.
In this engraving, A represents the work which is held down
by straps or clamps. In many instances when the work is

BORING JIGS 197

provided with bolt and screw holes before being bored, these
holes are used for clamping the work to the jig. In some cases
it is important that the work be attached to the jig in the same
way as it is fastened to its component part in the machine for
which it is made, and also that it be located in a similar way.
If the work is located by V-slides when in use on the machine,
it is preferable to locate it by V's in the jig. In other cases
the locating arrangement for the work in the machine where
it is to be used may be a tongue, a key, a dowel pin, a finished
pad, etc. The same arrangement would then be used for locating
it in the jig. In Fig. i enough clearance is left at .5, at both
ends, to allow for variations in the casting and to provide space
for the chips; also, if the hole is to be reamed out, and the
reamer be too large to go through the lining bushing, then the
space left provides room for inserting the reamer and mounting
it on the bar. In nearly all cases of boring, a facing operation
of the bosses in the work has also to be carried out and pro-
visions must be made in the jig to permit the insertion of facing
tools.

A great deal of metal may be saved in designing heavy jigs
by removing superfluous metal from those parts where it does
not materially add to the strength of the jig. In Fig. i, for
instance, the jig can be cored out in the bottom and in the
side standards as indicated without weakening the jig to any
appreciable extent. The rib C may be added when necessary,
and when it does not interfere with the work to be finished in
the jig. It will be seen that extended bosses are carried out
to provide long bearings for the bushings. The bosses may be
made tapering, as shown, providing practically the same stiff-
ness as a cylindrical boss containing considerably more metal.
Finished bosses should be located at suitable places to facilitate
the laying out and the making of the jig, as shown at D. The
finished faces of these bosses are also of advantage when lo-
cating the jig against a parallel, when it is not provided with a
tongue for locating purposes.

In some cases bosses are placed where measurements may be
taken from the finished face to certain faces of the work, in

198

JIG DESIGN

which case the finished bosses, of course, must stand in a cer-
tain relation to the locating point; such bosses are indicated
at E, from which measurements B can be taken to surfaces G
on the work. The three lugs H are provided for clamping pur-
poses, the jig being clamped in three places only to avoid unneces-
sary springing action. If the jig is in constant use, it would be
advisable to have special clamping arrangements as component
parts of the jig for clamping it to the table, thereby avoiding
loss of time in finding suitable clamps.

The walls or standards K of large jigs of this type are fre-
quently made in loose pieces and secured and doweled in place.
In such a case, the most important thing is to fasten these

1 pf—

Fig. 2. Simple Design of Adjustable Boring Jig

members firmly to the base, preventing shifting by tongues,
keys, or dowels. It is evident that, when the standards are
made loose, it is easier to finish the pad of the base, and this
is of importance, particularly when difficult locating arrange-
ments are planed or milled in the base; the patternmaker's
and the molder's work is also simplified. As a rule the standards
are screwed to the base permanently and then the bushing
holes are bored. In some cases, however, it may be easier to
first bore the hole in a loose part, and then attach it to the main
body.

Adjustable Boring Jigs. — When boring jigs are designed for
machine parts of a similar design but of different dimensions,
arrangements are often made to make one jig take various
sizes. In such a case, one or both standards may have to be
moved, and extra pads are provided on the face. This shifting

BORING JIGS

199

of the standards will take care of different lengths of work.
Should the work differ in height, a blocking piece may be made.
Sometimes special loose brackets may be more suitable for
replacing the regular standards for shorter work. If there is a
long distance between two bearings of the work, a third standard
may be placed in between the two outside ones, if the design
of the bored work permits; this may then be used for shorter
work together with one of the end standards. In Fig. 2 is
shown an adjustable boring jig. Here the jig consists of two
parts A mounted on a common baseplate or large table pro-
vided with T-slots. The work B is located between the standards.
A number of different standards suitable for different pieces of

Fig. 3. Jig located on and supported by the Work

work may be used on the same baseplate. The jigs or stand-
ards are held down on the baseplate by screws or bolts, and gen-
erally located by a tongue entering the upper part of the T-slots.
Boring Jig supported on Work. — Boring jigs are frequently
made which are located and supported on the work. Fig. 3
shows such a jig. The work At which in this case represents
some kind of a machine bed, has two holes bored through the
walls B and C. This jig may guide the bar properly if there
be but one guide bushing at E, but it is better if it can be ar-
ranged to carry down the jig member D as indicated to give
support for the bar near the wall B. It may sometimes be
more convenient to have two separate jigs located from the
same surfaces on the top or sides. In other cases it may be
better to have the members D and E screwed in place instead

13 J

2OO

JIG DESIGN

of being solid with F, and in some cases adjustable. Of course,
these variations in design depend upon the conditions involved,
but the principles remain the same. The jig or jigs are held
to the machine on which they are used by clamping arrange-
ments of suitable type.

Jigs for Supporting Bar on One Side of Hole Only. — The
type of boring jigs previously described supports the bar in
two or more places, and the cutting tools are placed at certain
predetermined distances from the ends of the bars, depending
upon the shape and size of the work. Sometimes it may prove
necessary, however, to have a cutting tool inserted just at the
end of the bar. For example, a boring jig may consist of

Fig. 4. Examples of Guiding Arrangements where no Support is obtainable on
One Side of Hole to be bored

simply one bracket as shown at the left in Fig. 4. A very long
bearing A is then provided so as to guide the bar true. The
arrangement shown at the right in Fig. 4 is sometimes used to
insure a long bearing for the bar. A special bracket E is mounted
on the jig and bored out at the same time as the jig proper is
machined. This provides, in effect, two bearings. In these
cases bars with a cutting tool at the end are used. There are
several reasons why a boring jig of this kind may be required.
For instance, there is a wall B immediately back of the wall C
in which the hole is to be bored. Other obstacles may be in
the way to prevent placing a bearing on one side of the hole to
be finished. Instead of having a space D between the jig and
the work, the jig can oftentimes be brought up close to the
work and clamped to it from the bushing side.

Each of the different holes in boring jigs has, of course, its
own outfit of boring-bars, reamers, and facing tools. In making

BORING JIGS

2OI

the jig it must be considered whether it will be used continu-
ously and what degree of accuracy will be required. When
extreme accuracy is required there should be a bar provided
with cutting tools for each operation to be performed. It is
cheaper, of course, to use the same bar as far as possible for
different operations, and ordinarily, satisfactory results are
obtained in this way. It is desirable to have bushings fitting

Fig. 5. Jig for Boring Holes located at an Angle to Each Other

Fig. 6. Diagram illustrating Principle of Multiple-bar Boring Jig

each bar, but often this expense can be reduced by using the
same bushings for bars having the same diameter.

When Holes are not Parallel. — It sometimes happens that
one or more holes form an angle with the axis of other holes in
the work to be bored. In the jig shown in Fig. 5, the bushings A
guide one bar for boring one hole and the bushings B the bar
for boring another hole, the axis of which is at an angle with
the axis of the first hole in the horizontal plane. Then an
angle-plate C can be made in such a manner that if the jig is
placed with the tapered side of plate C against a parallel, the
hole B will be parallel with the spindle. This arrangement

202

JIG DESIGN

may not be necessary when universal joints are used between
the spindle and the bar.

Jigs for Multiple Boring. — As a rule but one hole is bored
out at a time, owing to the fact that machines for boring
generally have but one spindle. Several holes, however, could
be bored out in a large-size multiple-spindle drill, in which
case the jigs naturally ought to be designed somewhat stronger.
Another method of designing jigs for boring two or more holes

Fig. 7. Jig for Boring Holes through Work both from Sides and Ends

at the same time is illustrated in Fig. 6, the outlines only being
shown in this illustration. The gear-box A contains the main
driving gear which is mounted on a shaft B which, in turn, is
driven by the spindle of the machine. The gear on shaft B
drives the gears and shafts connected with the boring bars
passing through the bushings C, D, E, F, G, and H. The gears
are proportioned according to the speed required for each bar,
which in turn is determined by the sizes of the holes. The
housing or gear-box A slides on a dovetail slide K. A particu-
larly good fit should be provided, and the gear-box can be fed
along in relation to the work either by table or spindle feed. If

BORING JIGS 203

boring operations are to be performed in two directions, a jig
on the lines indicated in Fig. 7 is designed. This jig may be
mounted on a special revolving table permitting the work and
the jig to be turned and indexed so as to save resetting and
readjusting the work and jig when once placed in position on
the machine.

The foregoing outline of boring jigs illustrates only the funda-
mental principles involved, it being considered more important
to state the fundamental principles in this connection than to
describe complicated designs of tools in which the application
of such principles may be more or less obscure or hidden.

Fig. 8. Example of Small Boring Jig, with Removable Leaf for
Holding Guide Bushings

Boring Jig Designs. — In Fig. 8 are shown two views of a
small jig supported directly on the work to be bored. This jig
is used for boring out a cross-slide carriage, and is located on
the work by the dovetail slide and held in place by the two
set-screws A. The two bushings B are driven into the solid
part of the jig and the two corresponding bushings C are placed
in the loose leaf D which is removed when the jig is placed in
position on, or removed from, the work. The two set-screws A
do not bear directly on the side of the carriage, but are provided
with brass or steel shoes. The leaf D cannot be attached perma-
nently to the jig and simply swung out of the way when the
jig is located on the work, because it could not be swung in
place after the jig is applied on account of the small clearance

204 JIG DESIGN

in the cross-slide carriage. The leaf is therefore made loose,
which is an objectionable feature, but lugs have been carried
up on the casting on both sides of the leaf as shown, to give
good support; these lugs are carefully finished to fit the leaf,
and the latter is located and held in place by ground plugs.

In Fig. 9 is shown a boring jig which receives the work A
between two uprights. The work in this case is the tailstock
of a lathe where two holes B and C are to be bored out. The
bottom surface of the tailstock is finished before boring, and
is located on the finished bottom of the jig by means of a key

Fig. 9. Common Type of Medium-size Boring Jig

and keyway. The keyway is cut in the jig and is a little wider
than the key in the work, and the set-screws D bring the key
against one side of the keyway, that side being in accurate
relation to the hole B to be bored in the tailstock. Longi-
tudinally the work is located by a stop-pin, against which it is
brought up by a set-screw from the opposite side. The tail-
stock is held to the jig by bolts E exactly as it is held on the
lathe bed.

The placing of the set-screws D at different heights is one
of the features of the jig; this makes it possible for the jig to
take tailstocks of various heights for different sizes of lathes,
raising blocks being used for the smaller sizes. The raising

BORING JIGS 205

blocks are located exactly as the tailstock itself, so that the
work placed on them will come in the same relative position to
the uprights of the jig whether the work rests directly on the
jig bottom or on the raising pieces. The two finished strips F
are provided for facilitating the making of the jig, and the lugs G
for the clamping down of the jig to the boring machine. The
jig, however, can also be clamped to the boring machine table
as shown in the illustration. At H is a liberal clearance between
the work and jig, allowing ample room for the inserting of
facing cutters, reamers, and boring tools. Ribs are provided
for strengthening the jig, as shown.

Fig. 10. Large-size Boring Jig made from a Solid Casting

Fig. 10 shows a large-size boring jig made from a solid cast-
ing. In this case the work to be bored out is the head of a
lathe. It is located and clamped to the jig in a way similar
to that mentioned in the case of the tailstock; clamping it to
the jig in the same way that it is fastened to the lathe bed
insures that the effects of possible spring will be less noticeable.
Opinions differ as to whether it is good practice to make up a
jig of the size shown in one piece, the distance between the
standards A and B being from four to five feet, or whether it
would be better to make loose members located on a baseplate.
With loose members there is no assurance that the standards
are located correctly in relation to each other or to the work

206 JIG DESIGN

to be bored, and it involves more or less work to get the jig in
order. The jig in Fig. 10 does not need to be as heavy as would
be inferred from the illustration, because a large portion of
the bottom can be cored out.

Four-part Boring Jig. — The boring jig illustrated in Fig. 1 1
consists of four parts; the upright members A, B, and C, and
the baseplate D, which latter may be used for all jigs of similar
construction. This type of boring jig is used only for very large
work. In the case illustrated, large lathe heads are to be bored.
The work is located on the baseplate between the two members
A and C. The member B is only used when the distance be-

Fig. 11. Boring Jig consisting of Baseplate and Separate Removable
Uprights carrying the Guide Bushings

tween A and C is very long, so that an auxiliary support for
the boring-bar is required, or when some obstacle prevents the
bar from passing through the work from one of the outside
members to the other. As a rule these members are located
on the baseplate by a tongue fitting into one of the slots as
shown at E. The members are brought as close as possible
to the work, sufficient space, of course, being permitted for
the cutting tools to be inserted. The standards are cored out
and ribbed and lugs provided so as to give the bearing bushings
long and substantial support. Good results will be obtained

BORING JIGS

207

with this type of jigs provided they are carefully set up on
the baseplate. At F in the member B is shown a boss; this
is provided with a tapped hole for a hook or eye-bolt to facili-
tate moving the jig member by an overhead crane. The other
members have tapped hole on the top for the same purpose.

Alignment of Jig when Holes are at an Angle. — In Fig. 12
is shown a boring jig for boring out the top frame A for adial
drills. The design of the jig is simple, but effective; the hole

Fig. 12. Jig having Wedge-shaped Locating Piece for Boring Holes
at an Angle

B is parallel with the finished side C of the jig and is bored out
after the jig has been brought up square against a parallel and
strapped to the machine table. The hole D is bored at an
angle with the hole B, and the setting of the jig for the boring
out of this hole is facilitated by providing a wedge-shaped piece
E of such an angle that the jig will be set in the proper position
when moved up against the wedge. If universal joints are
used for connecting the boring-bar with the driving spindle,
the setting of the work at an angle could be omitted, although
it is preferable even when using universal joints to have the
boring-bars as nearly as possible in line with the spindle. This
eliminates a great deal of the eccentric stress, especially when
taking a heavy cut with coarse feed.

208

JIG DESIGN

Using Work to Guide Boring-bar. — Boring operations are
sometimes carried out using parts of the machine itself as guid-
ing means for the boring-bars, and in some instances it is very
essential that boring operations be performed in this way in
order to obtain perfect alignment. In Fig. 13 is shown a ma-
chine bed with the headstock solid with the bed. In the top
view is shown a method for boring out a hole at B by the use
of two jigs C and D which are located on the V's of the machine
and held down by hook-bolts. If the hole B only passes through
the part E of the head this would be the preferable way of

Fig. 13. Example illustrating Use of Work as a Guide for the Boring-bar

boring it. In some instances, however, the hole B may be
required to be in alignment with the holes in a carriage or in
a bracket as at F and G. These holes, of course, can then be
used to great advantage as guiding means. Should the holes
be too large to fit the boring-bar, cast-iron bushings can be
made to fit the holes and the bar. The front elevation in Fig. 13
shows how a cross-slide carriage and apron 7, which has a hole /
in line with the holes in bearings K, L, and M, and travels
between K and L, can be bored out by using the brackets
K, L, and M to guide the boring-bar. By keying the traveling

BORING JIGS

209

part / close to the bracket during the boring operation, as
illustrated, accurate results will be obtained. It is evident that
two of the bearings could be bored out by using the finished
bearing and the traveling part / as guiding means. Arrange-
ments of this kind usually save expensive tools, and often give
better results.

Fig. 14. Combined Drilling and Boring Jig used with a Horizontal
Drilling and Boring Machine

Fig. 15.

Another View of the Jig in Fig. 14 — Note that Holes are
drilled or bored from all Sides

Combination Drill and Boring Jig. — Jigs for performing
both drilling and boring operations are frequently used to
great advantage. Combination jigs are sometimes used, how-
ever, when the operations can be more easily performed in two
separate jigs. For some classes of work it is advisable to have
a jig for the boring alone; the bored holes are then used for

210 JIG DESIGN

locating the work in a separate drill jig. In other cases it may
be better to do the drilling first and locate the work for the
boring operations from the drilled holes. The designer should
decide which method would be preferable, considering the time
required and the accuracy of the work. It is impossible to give
any definite rules for this work; but it may be said that com-
bination jigs should be used only when the drilled and bored
holes have nearly the same diameters. As a general rule, when
the holes are of widely different diameters, two jigs are prefer-
able. For example, if a few holes of small diameter for holding
a collar or bracket were located around a large bored hole,
and were drilled with the same jig used for the large hole, the
jig, when used on a small drill press, would be entirely too heavy
to manipulate. It is likely that in such a case a small separate
drill jig could be attached directly to the work. In many other
cases, however, it will prove a distinct saving to combine the
boring and drilling jig in one.

In Figs. 14 and 15 is shown a combination drill and boring
jig of large size. The work consists of a headstock for a lathe
with a number of holes to be drilled. The large holes B, Fig. 15,
at both ends of the headstock are cored as usual, and allow the
boring bar to enter for taking the roughing cut. The holes
at C and D are opened up by drills previous to the boring opera-
tion. As there is considerable distance between the end of the
headstock and the uprights of the jig, long bushings are used
to give the tools a good bearing close to the work. Both the
drilling and boring operations may be performed on a hori-
zontal boring and drilling machine. As the horizontal boring
and drilling machines usually have adjustments in all direc-
tions, the only moving of the jig necessary is to turn it around
for drilling the holes on the opposite sides.

CHAPTER IX
MILLING AND PLANING FIXTURES

Milling machines are now used for so many different purposes
that the fixtures used for holding parts to be milled differ con-
siderably in form and size, and there are several distinct types.
The simplest form of milling fixture is represented by the type
which simply holds and locates a single piece for a milling
operation. Then there are multiple or gang fixtures for hold-
ing a row of duplicate castings or forgings. This type may be
intended either for machines having a straight-line feeding
movement or a circular motion, as in the case of machines
designed for "continuous milling." Other milling fixtures,
which often are more complicated in design than the work-
holding fixtures, are arranged to hold the work in different
positions either for milling surfaces which are at an angle, or
for milling at various points around a circular part. The path
followed by the milling cutter is also controlled by some fix-
tures, especially in connection with profile milling; or the fixture
may be constructed to give the work a rotary feeding move-
ment as when milling a curved slot or groove on a cylindrical
part. Some idea of the variation in different types may be
obtained from the designs illustrated in this chapter.

Care should be taken to design milling and other fixtures in
such a way that the parts to be machined will be properly
located, and so that the operator who uses the tools cannot
get the work in wrong and thus spoil the parts. The fixture
should be easily loaded and unloaded, and it should be as open
as possible, to make cleaning easy and to prevent pockets for
chips. Hardened steel seats should be ground parallel with
the base after assembling, to obtain the best results. To bring
the cost as low as possible, the tool parts should be standardized
wherever practicable. The bodies and bases of fixtures should

212

JIG DESIGN

be made of cast iron and kept in stock in various sizes to meet
the requirements of the shop whenever this is practicable.
Clamping cams, dowel pins, bolts, and screws should be made
up in large quantity, and steel seat blocks, straps and other
steel parts should be made of standard stock sizes, if possible,
to prevent unnecessary machining.

Fig. 1. Detachable Vise Jaws for Use in cutting off Bar Stock

HARDEN SCREW AND NUT

Machinery

Fig. 2. Straddle-milling Fixture

Detachable Jaws for Vise. — The cheapest kind of milling
fixture that can be built is a pair of detachable vise jaws, as
shown in Fig. i. These jaws are made of cold-rolled steel and
casehardened. They can be removed from the vise quickly
and replaced by other jaws. It is advisable, however, to use
vise jaws only where great accuracy is not required, such as

MILLING FIXTURES

2I3

when cutting to length or milling clearance cuts. The jaws
here shown are used for cutting off pieces from a bar of stock,
which is pushed up against the stop and then cut off to the
desired length.

Fixture for Milling to Given Length. — When accuracy in
length is essential, a fixture like the one shown in Fig. 2 can be
used to advantage. The part to be machined is cut to the
approximate length in vise jaws or with a power hacksaw and
then straddle-milled in the fixture. Here it is located between
the two pawls B and clamped in place by the strap and cam.
On the arbor shown in Fig. 3 are mounted two steel disks A
about | inch larger in diameter than the two side milling cutters.

2 STANDARD DISKS— C. R. S.

j— , ,__, ^^ CASEHARDEN

IS'

STANDARD MILLING ARB

MAKE OTHER SPACERS

i A

TO SUIT

Machinery

Fig. 3. Arrangement of Cutters used with Fixture shown in Fig. 2

When the fixture is fed underneath the arbor, these disks depress
the pawls and give clear passage for the cutters. On the same
arbor can be mounted other cutters to suit the work. This
arbor should never be taken down, as it is important that the
distance between the straddle-mills be kept constant; the
cutters should be ground on the arbor.

Duplex Fixture. — The milling fixture shown in Fig. 4 is
made for machining two parts in one operation. On the cast-
iron base is mounted a double seat block and the seats are
ground after assembling. The parts to be milled are clamped
in place by cam binders at each end and two straps. By using
set-screws in the straps, accuracy in making the cams is not
necessary, and wear on the cam faces can be taken up by these
adjusting screws.

214

JIG DESIGN

Adjustable Fixture for Angular Work. — Occasionally in
every line of manufacture there are parts which are simple in
appearance, but difficult to machine. Fig. 5 shows a part of
a belt shifter used on an automatic machine, the makers of
which use eight different shaped pieces of this kind. The stock
is flat and one-half inch thick. If the sides of the slots were
perpendicular, the manufacture of these pieces would be very
simple, but the sides are not perpendicular, and the angles
they form with the bottom differ with each different shaped
piece. As a result, these pieces are difficult to manufacture
without the proper form of fixture.

TWO STOP PINS

Machinery

Fig. 4. Fixture for Machining Two Parts in One Operation

The fixture shown in Figs. 6 to 8 consists of two parts A
and B, which are clamped together, when in the proper posi-
tion, by bolts passing through holes in the lower casting A
and slots in the upper casting B. A tongue planed in the bottom
of the base A fits a slot in the milling machine table, to which
the base is bolted. The upper part B is turned to fit the lower
part so that no gib is required. The parts to be milled are held
in place by a set-screw, which is not shown. Each shape has
its own number, and these numbers are stamped upon the
top surface of the base A. The upper part of the fixture can
move in either direction from the center, so that by placing

MILLING FIXTURES

2I5

Fig. 5. Belt Shifter Parts held in Adjustable Fixture shown in
Figs. 6 to 8, inclusive

Fig. 6. Milling Steps D and E of the Part shown in Fig. 5

the locating pin C in the proper hole, as shown by the number,
the fixture can be quickly set for machining any shape. Fig. 6
shows the different size cutters milling projections D and E,
Fig. 5; in Fig. 7, the central slot F, Fig. 5, is being cut. Fig. 8
14 J

2l6

JIG DESIGN

Fig. 7. Milling Central Slot in Belt Shifter Part

Fig. 8. Position of Fixture for Cutting Angular Side of End Slot

MILLING FIXTURES

217

shows how the angular slots may be finished. This type of
fixture can be used for all kinds of angles, as holes can be placed
where desired from zero to its full capacity.

Fixture arranged for Lateral and Angular Adjustment. — A
fixture designed for milling the sides of the block shown in
Fig. 9 is illustrated by the plan view, Fig. 10. Three operations
are involved; the parallel sides A are milled by means of the
straddle cutters and the two sides B and C are then milled in
two subsequent operations. These three operations are all
performed without requiring more than one setting of the
work. The block is cut off from bar stock,
and drilled and counterbored to receive two
fillister-head screws which hold it in place
on the machine of which it forms a part.
These holes are also utilized for holding the
block in position on the fixture.

The milling fixture consists of an upper
plate A which is pivoted on the stud B.
This stud is mounted in the cross-slide C
which operates on the base D. The plate
A is provided with two tapped steel bush-
ings which are a forced fit in holes drilled
and counterbored for the purpose. These
bushings receive the two screws which
secure the work in position on the fixture, their purpose being
to prevent the rapid wear of the threads which would take
place if they were tapped directly into the cast iron. The fix-
ture is shown in the illustration set in position for milling the
parallel sides A of the work. There are two tapered pins E
and F which are used for locating the work in the required posi-
tion. For milling the parallel sides of the work, the pin F is
inserted in the hole N to locate the cross-slide C in the required
position. Similarly the pin E is located in the central hole to
locate the swivel plate A . These pins are merely used to locate
the fixture, the bolts G and H being provided to secure it in
the required position. When the fixture is set for milling the
angular side C of the work, the pin E is inserted in the hole

Fig. 9. Piece which is
milled on Sides A, B,
andC

2l8

JIG DESIGN

/ and pin F in the hole 0. This sets the swivel plate A at
the required angle and also locates the cross-slide C at the
required distance off center to enable the work to be milled by
the outer edge of the cutter. After this operation has been com-
pleted the swivel plate A is swung over to enable the pin E to
enter the hole K. Similarly the cross-slide C is moved so that
the pin F will enter the hole M. This brings the work in posi-

Fig. 10. Plan and Sectional Views of Milling Fixture for Piece shown in Fig. 9

tion to enable the angular side B to be milled by the outer edge
of the other cutter on the arbor.

Lever-operated Fixture for Milling Oil-groove in Bushing. —
Figs, ii and 12 show a special milling fixture designed to hold
the brass bushing A while milling the oil-groove B. The fixture
with the bushing in place may be seen in Fig. n. The detailed
construction of the fixture, however, will be more clearly

MILLING FIXTURES 219

understood by referring to Fig. 12. The fixture consists of a
base C which carries a slide D, set at an angle of about 30
degrees with the base. The V-block E supports the work,
which is held between the angle-plates F and G. Plate F forms
a stop for the work, while plate G is milled to make provision
for the insertion of the wedge H. The hand-lever / is more
clearly shown in Fig. n. To operate this fixture, which may
be used on any milling machine, the cutter K is placed in the
horizontal spindle of the machine, and the fixture set up facing
it. The method of holding the bushing during the machining
of the groove is apparent from the illustrations, which show
it seated in the V-block and held firmly between the angle-

Fig. 11. Fixture for Holding Bushings when Milling Oil-groove

plates by the wedge. After the wedge has been driven into
place, the cutter is fed into the work to the required depth,
and slide D is operated by means of hand-lever / advancing
the bushing until the proper length of groove has been milled.

This fixture could no doubt be greatly improved upon by
the addition of better means of clamping the work, and could
also be made to handle a wider range of work by the addition
of suitable stops for controlling the length of the cut. How-
ever, for the particular work for which the fixture was designed,
this was not thought necessary, as the quantity of pieces to
be machined did not warrant it.

Indexing Milling Fixture for Roller Separator. — The bronze
roller separators seen in Fig. 13 form part of the roller bear-
ing of a gun mount upon which the carriage turns when train-

22O

JIG DESIGN

ing the gun or adjusting it horizontally. These separators have
twenty-four holes, and opposite holes must be in alignment
and in a radial position, as otherwise there will be a creeping
action of the rollers relative to their bearing rings or tracks.
A milling machine equipped with a simple type of indexing
fixture is used for this work. The base A of the fixture is bolted
to the machine table and the upper part B is free to revolve.
This revolving member has accurately spaced holes which are
engaged by indexing plunger C. After the holes have been

Machinery

Fig. 12. Detail View of Milling Fixture shown in Fig. 11

drilled and reamed, they are counterbored by the use of suit-
able tools. The separator rings are located on the fixture by
means of the central bore.

Indexing Fixture for Milling Clutches. — The design and
construction of a special form of fixture used for cutting the
clutches on transmission drive pinions and sliding gears is
shown in Fig. 14. This fixture consists of a frame A into which
the spindle B is fitted. The spindle is designed to serve as
a collet chuck on the upper end and is arranged to carry the
large index plate C at its lower end. The index plate has a
series of holes E drilled in it at a convenient angle to receive

MILLING FIXTURES

221

the handle D. To turn the spindle, it is merely necessary to
withdraw the spring-supported locking bolt seen at the right-
hand side of the base, by means of the small lever provided
for that purpose, and move the index plate around by means
of the handle D which passes through an elongated slot.

Fig. 13. Fixture for Drilling, Reaming, and Counterboring Holes in Roller
Bearing Separator Rings

The method of chucking the pinion shaft G is clearly shown
and will need little description to make it clear to any mechanic.
It will be seen that a small collar H rests in a hole at the bottom
of the spindle; this collar receives the downward thrust of the
work and also serves the purpose of locating the lower end of
the work to bring it exactly perpendicular. In using this

222

JIG DESIGN

fixture it is customary to put a sheet-metal washer between the
lower face of the pinion and the top surface of the chuck ring I
in order to keep chips and oil from running down into the
dividing-head.

When milling the clutch gear /, the split collet is replaced
by the expansion chuck K. The body of this chuck fits into
the spindle and is locked in position by the chucking ring 7.
The work is held on this chuck by expanding it by means of
the taper-headed screw L, which is turned by a square key.

Machinery

Fig. 14. Cross-sectional View of Fixture for Milling Clutches and
Details of Work-holding Arbors

The hardened steel collar M is fitted on the chuck to provide
a good bearing surface and resist wear. The clutch gear is
shown in position on the chuck by dotted lines.

Eight cuts are required to complete the milling operations
on one of these clutch gears, and consequently it is necessary
to use an eight-point index plate. After setting to bring the
cutter to the required depth, the milling machine saddle is
moved in until one edge of the cutter registers with a point
o.oio inch to the left of the center; four cuts are then made,
completing one side of the clutch teeth. To mill the other side
of the teeth, the milling machine saddle is moved out until
the other side of the cutter registers with a point o.oio inch

MILLING FIXTURES

223

to the right of the center. The head is then indexed | revolu-
tion to mill the side of the first tooth, and then J revolution
for taking each of the three remaining cuts. The clutch teeth
are cut a little off center in order to give the clutches the re-
quired amount of clearance.

The ideas embodied in the design of this special fixture may
suggest other uses for a tool of this kind where it is required
to perform milling, drilling, and other operations on work for
which the regular milling machine dividing-head is not suitable.

Fig. 15. Continuous Milling Fixture for Liberty Motor
Connecting-rods

Continuous Milling Fixture. — Fig. 15 shows a continuous
milling fixture which is employed for the milling of connecting-
rods on a double-spindle vertical milling machine. Four sur-
faces on the rods are milled at once, the top and bottom surfaces
at each end being milled simultaneously. The main spindle,
which is provided with two cutters, one for the upper and one
for the lower surface, mills the outer end of the rod, while the
auxiliary spindle with cutters mounted in a similar manner
mills the inside end of the rods. Fourteen connecting-rods are
mounted in the fixture at a time, and as the fixture rotates on
the table, the finished rods are taken out and new rods are
inserted by the operator while the work progresses. Every
other jaw for holding the connecting-rods is fixed, while every
alternate jaw is pivoted at one end. By clamping against one

224

JIG DESIGN

rod with a clamping screw at the extreme end of the pivoted
clamp, pressure is brought to bear upon the ends of the con-
necting-rods on each side of the pivoted clamp, thus making
the clamping very rapid. At the inside end, one clamp also
holds two rods in place. This clamp is provided with a small
pin which fits into a slot in the clamping stud, so that, when
tightened, the clamp must always be in one position and cannot
come out far enough to interfere with the milling cutters.

Fig. 16. Fixture for Rough-mining a Circular Slot in Sight-bar

Radial Milling Fixtures. — Radial fixtures are so called
because they are used for machining parts to a given radius.
In. general, the work-holding part of the fixture is either pivoted
or is guided by a curved track so that it is given a circular mo-
tion when in use. Some ingenious radial fixtures used for
machining the sight-bars of naval gun mounts, at the plant of
the Mead-Morrison Mfg. Co., East Boston, Mass., will be
described. The radial or circular surface of the sight-bar must
be so nearly perfect that the sight may be operated through
its complete range of adjustments without any binding action
and without perceptible lost motion between the moving parts.
The curved surfaces of the sight-bar and of the bearing in the
sight-bar bracket must be exactly concentric with the axis

MILLING FIXTURES

225

of the pivot about which the sight moves in elevation. These
and other exacting requirements make this a very interesting,
although difficult, part to produce on an interchangeable basis,
and it was necessary to design special radius milling fixtures.

Radial Fixture for Rough-milling Slot. — The slot which is
milled in one side of the sight-bar is rough-milled as illustrated

Fig. 17. Fixture for Milling Curved Slot in Sight-bar Bracket

in Fig. 1 6. This is the type of fixture which has a curved track
that causes the work-holding member to follow a circular path
as the work feeds past the cutter. The sight-bar A is held on
a movable part which has a slot B in the rear side of the same
radius as the slot to be milled. A block C, which is free to
swivel and is pivoted to a stationary part of the machine, en-
gages slot B. The cross-feed screw in the knee is removed, and
as the table is fed in a lengthwise direction, a slot is milled to

226 JIG DESIGN

the same radius as the slot B in the fixture. A weight is at-
tached to the saddle of the machine by means of a wire cable
which is connected at D. The object of using a weight is to
hold block C in contact with the slot on one side, and thus by
eliminating all play it is possible to secure a higher degree of
accuracy. A two-lipped end-mill is used for this operation.
The slot is milled 0.8 inch wide and if inch deep.
Another radial fixture of the general type just described is

Fig. 18. Radial Milling Fixture used for Different Operations on Sight-bar

shown in Fig. 17. This fixture is for the bronze bracket through
which the sight-bar slides when being elevated or lowered.
It has a curved slot which must be milled to the same radius
as the sight-bar to avoid any cramping or binding action. A
finished surface on the bracket A is clamped against a top plate
or bridge B of the fixture, and it is further located by a plug C
at the right. The base of the fixture fits between curved tracks
or guiding strips D. At one end of the fixture a transverse
slot is formed, and this is engaged by a block pivoted to a nut
through which the feed-screw passes. The feed-screw is con-
nected by gearing E with the regular feed-rod of the machine,

MILLING FIXTURES 227

and as the movable section of the fixture is fed along, a slot is
milled to the same radius as the tracks.

Pivoted Type of Radial Fixture. — The curved sides of the
sight-bar and also the beveled surfaces along one edge are
milled by means of a radial fixture of the type shown in Fig. 18.
This general style of fixture is used extensively in connection
with other operations on the sighting mechanism. It has a very
heavy base casting Aj which is bolted to the table of the ma-
chine. The sight-bar B is held on the swinging part C of
the fixture, which is pivoted at D. At the work-holding end
of the swinging member there is a swiveling nut through which
passes a feed-screw. This feed-screw is connected by gearing
located at the end of the table with the regular feed-screw of
the machine, the nut in the milling machine having been re-
moved j consequently, when a sight-bar is being milled, the
part C of the fixture is given a circular movement about the
pivot D as the power feed traverses it from one end of its swing
to the other. The illustration shows the machine milling the
beveled edges on the top of the sight-bar. When the sides
are being milled, the cutter shown at E is used. After one side
has been milled, the stops F are transferred to the opposite
side so that they will not interfere with the cutter. The gage
used for testing the radius of the inner surface forms part of
the fixture, and consists of a bar G which is free to slide through
a block H. This block is also free to turn about the same pivot
which is used for the swinging part of the fixture. The radius
of the sight-bar is tested by bringing the gage point into con-
tact with it and then noting the position of the end of bar G
relative to the outer surface of block H. When the end of the
bar and the surface of the block are exactly in the same plane,
as indicated by tests made with a dial gage, the work is correct.

The sight-bar is located in the fixture by the finished face of
the head, which also serves as a common locating point for
many other operations. There is considerable overhang of the
fixture relative to the machine table, and in order to avoid
sag, the overhanging part is counterbalanced by a heavy weight
attached to one end of the wire cable / which passes over pulleys
fastened to the ceiling.

228

JIG DESIGN

3
*

MILLING FIXTURES 229

Radial Fixture for Gear-cutting Operation. — The sight-bar
and the other parts of the sight mechanism which are attached
to it are elevated or lowered through a pinion which engages
teeth cut on one side of the sight-bar. These teeth must be
very accurately spaced; in fact, the total tolerance or allow-
able error in the fifty-five teeth of the sight-bar is only 0.0005
inch. The fixture used for milling these gear teeth is illustrated
in Fig. 19. The gear teeth on the sight-bar do not form a rack,
but rather the segment of a gear, since the pitch line is an arc;
therefore, the radial type of fixture is employed. The base A
is bolted to the machine table, and the swinging part B is
pivoted at the rear end. Beneath this swinging part there is
a segment of a worm-wheel, and meshing with it a worm car-
ried by the shaft of the indexing mechanism. The indexing
crank C connects with this worm-shaft through spur gearing.
The sight-bar is clamped to an adapter plate, which is replaced by
another adapter when the same fixture is used for milling opera-
tions on the yoke. The sight-bar is located in part by the finished
surface of the head, as is the case in the other operations.

As it would be difficult, if not impossible, to construct a
large fixture of this kind and eliminate all measurable error,
the original inaccuracy is eliminated as far as possible in order
to reduce the error in spacing the teeth to a minimum. The
method of compensating for this original error is as follows:
When indexing the fixture a distance equivalent to one tooth
space, crank C is turned one revolution or until its spring-pin
again comes around into mesh with the hole in the disk shown.
Since there are 55 teeth in the sight-bar, and as the total original
error was a few thousandths inch large, this error is compen-
sated for by turning the indexing disk D backward an amount
equivalent to -^ of the original error. There are really two
indexing movements, therefore, for each tooth space, the same
as in compound indexing. A gear tooth caliper of the vernier
type is used for testing the tooth thickness; the spacing is
verified by placing pins between the gear teeth at each end of
the segment, and also at intermediate points, and then measur-
ing the distance between the pins by using a vernier caliper.
The counterbalancing weights are also used in conjunction

23°

JIG DESIGN

"8*8

MILLING FIXTURES

23I

with this fixture, the attached cables E and F passing over
pulleys above. These weights not only counterbalance the
overhanging parts of the heavy fixture, but also make it easier
to elevate the knee for feeding the cutter down past the work.

Radial Fixture having Hand- and Power-operated Feed. —
The yoke of the sight mechanism is a cast-steel member which
carries the telescopes at its forward end and is attached at the

Fig. 21. Fixture for Milling Curved Openings in Bronze Recoil Liners

rear to the sight-bar. There are some radial milling operations
on the rear end of the yoke. The curved surfaces at the end
of the yoke are milled to the required radius by a type of fix-
ture which, in many respects, is similar to the radial designs
already referred to in connection with the sight-bar. The
base of the fixture (see Fig. 20) is bolted to the table of a column-
and-knee type of milling machine, and the upper part B is free
to swing about a pivot located at the required radial distance.
One radial milling operation is that of form-milling the worm-gear
segment in which worm teeth are cut later to mesh with a worm
which enables the yoke to be adjusted horizontally. Several

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232

JIG DESIGN

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MILLING FIXTURES

233

Profile Milling Fixture for Recoil Cylinder Liner. — An unusual
type of milling fixture, and one which proved very effective for
a contour milling operation on the bronze liners of recoil
cylinders, is illustrated in Figs. 21 and 22. The former illustra-
tion shows the fixture set up on a milling machine. This fixture
has a master sleeve or former A in which there is an opening
corresponding to the one to be milled in the recoil cylinder
sleeve B. A roller C, mounted upon a bracket secured to the
front of the machine, engages the opening in the former. The

Fig. 23. Fixture for Routing Oil-grooves on Two Bushings at One Time

master former and the recoil liner are caused to turn in unison
by a link D which, as clearly shown by the end view, Fig. 22,
is connected to the ends of extension arms on the former and
work-holding shafts. When milling the lower edge of the open-
ing, which is the operation shown in Fig. 21, the weight E is
swung over to the right, so that it tends to hold the former
firmly in contact with roller C. When the machine table is
fed in a lengthwise direction for milling this edge, the master
former and liner do not have any turning movement, since the
lower edge of the opening is straight. For milling the upper
or curved side, weight E is swung over to the left, and then the
curved part of the opening in the master former is held securely

234 JIG DESIGN

against the roller; therefore, when the milling machine table
is fed in a lengthwise direction, the former and liner turn in
unison as the curved section of the opening is milled. Two
lugs on the hub of the weight lever alternately engage a stop
as the lever is turned from one position to the other, and in
this way either the lower or upper sides in the master former
are held against the roller C. The liner has a similar opening
on the opposite side, which is milled by simply connecting the
upper end of link D with the opposite end F of the double
extension arm (see end view, Fig. 22).

Duplex Fixture for Routing Oil-grooves. — A duplex type
of fixture used for routing oil-grooves in bronze bushings is
shown in Fig. 23. The routing operation is performed on two
bushings simultaneously, and a drilling machine is used for
the operation. The oil-grooves of the bushings, in this par-
ticular case, extend around about two-thirds of the circum-
ference of the bushing and branch out into a Y-shape at each
end. The horizontal spindle of the fixture is rotated for feeding
the bushing past the routing tools, by handwheel A, which
serves to revolve a worm meshing with wheel B. The axial
movement of the fixture spindle is derived from cam grooves
on each side of gear B. The shafts C and D carrying the rollers
have rack teeth which engage the segment gears formed on
the pivoted lever E. By swinging this lever in one direction
or the other, the rollers are alternately engaged. When the
left-hand roller is engaged with its cam groove, the left-hand
branches of the Y-shaped oil-grooves on each bushing are
milled, and when the right-hand roller is moved inward the
right-hand branches of the oil-grooves are milled.

Planing Fixtures. — Fixtures for planing are as essential for
interchangeable manufacturing as are drilling jigs or milling
fixtures. Planing fixtures serve primarily the purpose of locating
and holding the work, but they are often provided with setting
pieces or templets which are used for setting the cutting tools
so that the work is always machined in a certain relation to
the locating means on the fixture itself. Some milling fixtures
also have this tool-setting feature.

The strength of fixtures should be governed by the kind of

PLANING FIXTURES 235

operation to be carried out on the work while in the fixture,
whether planing, milling, slotting, etc., and how much stock
is to be removed. A milling fixture, as a rule, must be made
stronger than a planing fixture, because a milling cutter or-
dinarily takes a heavier cut than a planing tool. Many of the
features often found on milling fixtures may be applied to planer
fixtures with whatever change may be necessary on account of
the particular operation required. As a rule, milling and plan-
ing fixtures are provided with a tongue or key in the base, for
locating them on the machine table. Suitable lugs should also
be provided for clamping the fixture to the platen.

The most commonly used fixture for planing, shaping, and
milling is the vise. Standard vises are indispensable in planer
or milling machine work or on the shaper, and by slight changes
they can be used for a large variety of smaller pieces. The
regular vise jaws are often replaced by false jaws, which may
be fitted with locating pins and seats, and held to the vise the
same as the regular jaws. Vises with false vise jaws are es-
pecially adapted for milling operations, but vises are not usually
employed for long work, special fixtures being commonly used.

Planing Fixtures for Lathe Carriage Casting. — Assume that
a set of planing fixtures for the piece shown in Fig. 24 is re-
quired. The work is a slide or carriage for a lathe. The finish-
ing marks given on a number of the surfaces indicate where the
work is to be finished. In the first place, it must be considered
from which sides to locate, and how to locate and hold the work
without springing it, and in what order the operations should
be performed to best advantage. Fig. 25 shows a fixture for
roughing out the ways on the bottom. The slide is located on
three fixed locating points A and the sliding point B. This
latter is adjustable in order to enable planing the slide as nearly
as possible to uniform thickness. Sometimes, if the parts A,
Fig. 24, bevel toward the ends, lugs G may be added; these
can then be finished and used for locating purposes. The car-
riage, as shown in Fig. 25, is further located against the pins C
in order to insure that the cross-slide of the carriage will be
square with the bottom ways. The slide is brought up side-
wise against the pin D, and then clamped down in convenient

236

JIG DESIGN

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Fig. 24. Lathe Carriage Casting — An Example of Work illustrating Points
in Planer Fixture Design

Fig. 25. Fixture for Rough-planing Ways for Carriage Casting

PLANING FIXTURES

237

places, the clamps being placed as near the bearing points as
possible to avoid springing. The reason for not having the
locating point D on the opposite side is that this side must be
finished at the same setting, as it is the front side of the carriage
and is finished for receiving an apron.

Fig. 26. Fixture for Planing Cross-slide Dovetail

The sides E and F of the fixture may be finished in a certain
relation to the locating points and to each other, and side E may
be made perfectly square with the locating points, so that, when
brought up against a parallel on the machine table, the ways of
the machined piece will be square with the ends. Side F may
be finished on the same taper as required for a taper gib.

JIG DESIGN

The fixture for the next operation is shown in Fig. 26. This
fixture is made to receive the carriage and locate it by the now
rough-finished ways; in this fixture, the cross-slide dovetail is
planed. The slide rests on four finished pads A, and the straight
side B of the ways in the slide brought up against the finished

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Fig. 27. Fixture for Finish-planing Bottom Ways

surfaces C. If no other part is available for clamping the fixture
on the machine table, lugs E are added. If there are no taper-
ing surfaces, the fixture can be located on the machine table
by a tongue or by placing a finished side against a parallel.
The slide or dovetail is now roughed out and it is usually suffi-
ciently accurate practice to finish it in the same setting, es-

PLANING FIXTURES 239

pecially as slides must always be scraped and fitted to suit the
machine on which they are to be used.

The next operation would be performed in the fixture illus-
trated in Fig. 27. The carriage is here located by the dovetail
and by the pin B, and held by a gib C, or by straps and screws,
as shown. It will be noticed that, with the given design, the
straps and screws must be removed each time a new piece is
inserted, which is an undesirable feature of the fixture. If
parts A in Fig. 24 project out too far, so that a light finishing
cut would cause springing, they are supported by sliding points
or other adjustable locating means.

If the dovetail in the slide had simply been rough-finished
in the fixture in Fig. 26, the finishing of the bottom ways could
have been done in the fixture in Fig. 27, and then, after having
finished the bottom ways in this fixture, the work could again
have been located in the fixture in Fig. 26, and the dovetail
finished; this might insure more accurate work in some cases.

In the case just described, the work requires three different
fixtures to be completed. The number of fixtures to use in
each case is entirely dependent upon the nature of the work.
When there is a large amount of work of the same kind to be
done, several fixtures of the same type are made up for the same
piece, and when in use these fixtures are placed in a row on the
table of the machine.

Gang-planing Fixtures. — It is very common in planer prac-
tice to locate a number of duplicate castings or forgings in a
row extending lengthwise of the table and then plane them all
at the same time. Gang planing is often done without a special
fixture, by simply clamping the work directly upon the table,
but fixtures make it possible to set up work more rapidly and
accurately. Besides many pieces are of such a shape that a
fixture is necessary in order to hold them in the correct position
for planing. An example of work requiring a fixture is shown
in Fig. 28. Twenty- three forgings are planed at one time and
four cutting tools are used, two being held in the side heads
while two are attached to the heads of the cross-rail. The forg-
ings are located at right angles to the length of the planer table

240

JIG DESIGN

I
§

PLANING FIXTURES

241

by the milled sides, one side of each bar being held against a
vertical surface on the fixture, as shown in the illustration.

Radial Planing Fixture. — A planer equipped with a special
radial fixture is shown in Fig. 29. An arm A is rigidly attached
to one of the planer housings and carries a shaft B which forms
the pivot for the swinging part C of the fixture. This swinging

Fig. 29. An Example of a Radial Type of Planing Fixture

member has a slot on the rear side which is engaged by a pivoted
block which moves to and fro with the planer table; conse-
quently, the sight-bar, which is held to the swinging member
in an upright position, follows a circular path and is planed to
a circular form, the radius of any surface being governed by the
horizontal distance from the cutting edge of the tool to the axis
of pivot B. This fixture is similar in principle to some of the
forms used in locomotive shops for planing the links of the valve-
operating mechanism.

CHAPTER X

ADJUSTABLE FIXTURES FOR TURRET LATHES AND
VERTICAL BORING MILLS

When pieces of the same type, but of various sizes, are to
be machined on the turret lathe or vertical boring mill, it is
sometimes desirable to design the tools and fixtures in such a
way that they can be adapted to handle the different pieces,
thus avoiding the necessity of providing a separate tool or
fixture for each piece. Naturally, when the production is large,
such a procedure as this would be unprofitable, because the
tools could only be used on one piece at a time, and a lot of
pieces of one size might be held up for a considerable time wait-
ing for a lot of another size to be machined. When, however,
the work comes along in lots of from 100 to 200 pieces, a great
saving in tool cost can be effected by the use of adjustable
tools and fixtures, providing the design of the parts is such that
it will permit of following this practice. Much depends upon
the shape of the work to be held and its machining requirements.

There are instances when the desired results may be obtained
by simple means, and there are other cases which require the
application of considerable ingenuity in order to avoid com-
plications in the design. Properly designed and carefully built
tools and fixtures of the adjustable type are profitable invest-
ments on certain classes of work, and their advisability should
be carefully considered when several pieces of the same general
type are to be handled. The greatest forethought is necessary
in designing fixtures of this kind, in order to make sure that
every point for every piece has received proper consideration.
There is probably no other type of fixture which requires so
much care in its design, and for that reason the important
points given herewith should be most carefully noted.

Important Points in Design. — i. The number of pieces to
be machined should be the first point considered, as this natu-
rally has an effect on the design of the tools and fixtures.

242

ADJUSTABLE FIXTURES 243

2. The largest and smallest pieces in the group should be
selected, and the machine on which the work is to be done
should be determined according to the sizes of these pieces.
If the variation in size is considerable, it may be economical
to do a part of the work on one machine and the remainder on
another, in which case the fixture should be so made that it
can be adapted for use on both machines. There may even be
cases when the range of sizes is so great that two or more fix-
tures may be necessary, one of which can be used on one machine
and the other on a different one; or they can be made inter-
changeable, providing the speeds on both machines give range
enough to handle the work. These points should be carefully
considered.

3. The accuracy required in the finished work should be
noted and care taken to provide means of upkeep on surfaces
or locating points that are subject to wear. There may be
occasional instances, on work requiring extreme accuracy, when
it may be necessary to provide means of adjustment for truing
up the fixture so that it will always run perfectly concentric
with the spindle of the machine.

4. Rigidity in work-holding devices and tools should receive
careful attention; and overhang from the spindle, turret, or
cut-off slide should be kept down to a minimum, so that chatter
will not result from lack of support. These points need more
consideration when the tools and fixtures are to be used on
the horizontal type of machine, than when a vertical machine
is to be employed.

5. Clamping devices for adjustable fixtures should be laid
out (by means of a piece of tracing paper) for each piece to
be handled, so that there will be no chance of clamps being too
long, too short, or improperly proportioned for some of the
work. Errors are very likely to occur in this part of the design
unless the greatest care is used; and there are also cases when
the work varies in thickness as well as in diameter; therefore,
this point must be carefully considered.

6. Provision for cleaning the fixture must be made, so that
all locating points and surfaces will be readily accessible. If

244 JIG DESIGN

several sizes of studs or locating rings are to be used, they must
be so arranged that chips and dirt will not interfere with the
proper location of the work. They must also be placed so that
they can be easily replaced or removed.

7. The adjustments which are necessary to provide for
handling various sizes of work should be carefully studied, and
suitable provision should be made so that the changes from one
setting to another will always be uniform, and variations in
the work cannot occur due to errors in adjustment. If necessary,
setting gages can be made for the various pieces to be handled,
or a separate set of screws or other adjustable locating members
can be made for each piece and properly stamped to avoid mis-
takes. The nature of the work has a great deal to do with the
method used to secure uniform adjustments, and specific cases
will be noted in following paragraphs.

8. Convenience and rapidity of operation should be given
consideration, and provision should be made for setting up
the work in as short a time as possible. The fixture should be
so arranged that the work can only be set up in the correct
way, and it should be as nearly "fool-proof" as possible.

9. The cost of the fixture should be kept down to the lowest
figure that is consistent with good design, because the number
of pieces to be machined is comparatively small. If the work
for which the fixture is made is of such a nature that it is not
likely to be changed, a little more latitude is permissible; but
as changes in design are always possible, it is advisable not to
make an elaborate fixture.

10. The safety of the operator should always be considered,
and projecting lugs, set-screws, or other parts which might
catch in his clothing should be eliminated from the design.
Other points in design not mentioned in the foregoing will be
specifically mentioned throughout this chapter; comments
will be made, and faulty points criticized and discussed.

The three- or four-jawed chuck is perhaps the most fre-
quently used of all the holding devices which are adjustable
to take various sizes of work. There are also collets of numer-
ous kinds, which are adjustable within certain limits, and step

ADJUSTABLE FIXTURES

245

chucks for work of a little larger size. For handling work in
the rough state, the three- or four-jawed chuck is adaptable
to a great range of sizes, without any changes in the chuck

Machinery

Fig. 1. Fixture for Holding Pot Castings on Horizontal Turret Lathe;
Different Clamping Collars are provided for Different Sizes of Work

jaws; but collets and step chucks require a change in jaws, or
a re-setting if much variation is found in the diameters of dif-
ferent pieces of work. The step chuck is more frequently used
for partly finished work, while collets are used for both rough

246 JIG DESIGN

and finished pieces — principally for bar work or something of
a similar character. When a round piece of work is to be made
up in several sizes and is of simple form, it may often be handled
to good advantage in a set of soft jaws applied to a three-jawed
universal chuck. These jaws are bored out on the machine
to the exact diameter of the finished work, and when set up on
the piece they present a good holding surface with sufficient
accuracy for the ordinary run of commercial work.

Adjustable Fixture for Holding Castings of Different Diam-
eters. — Fig. i shows at A and L the smallest and largest sizes
of castings to be machined on a horizontal turret lathe; and
there were two intermediate sizes which were also handled on
the same fixtures. A special nose-piece C is screwed to the
end of the spindle and has a hub at its forward end on which
the locating ring B (upper view) is fixed. The finished portion
of the work fits this ring at D and is drawn back against it by
the collar G; the rod E passes through the spindle and is pulled
back by means of a handwheel at the end, while the key F
prevents it from turning. The forward end of the rod is
threaded to receive the knurled finger-nut H which has a
spherical bearing in the collar G to equalize the pressure. In
setting up the work, the piece is placed on the locating ring,
the collar G is slipped over the end of the rod E and the
knurled nut H is rapidly screwed on with the fingers, after
which the handwheel at the end of the spindle is used to
tighten the collar. A long boring tool / is used to rough out
the shouldered portion of the work and to bore the bearing,
and it will be noted that although this tool has considerable
overhang it is well set up in the tool-holder K, and given addi-
tional strength by the use of two toolposts.

The larger piece L, shown in the lower part of the illustra-
tion, is set up on the ring M locating on the surface 0, which
has been previously bored. A larger collar N is used for clamp-
ing this piece. With the exception of the locating ring and
collar, all of the other parts of the holding device are the same
as in the preceding instance. Additional rings and collars for
the intermediate sizes make the fixture complete. It will be

ADJUSTABLE FIXTURES

247

noted that there are two holes in the front of the nose-piece,
which are so placed that a rod may be used to drive off the
locating rings when changing over the fixture for another size
of work. This fixture is simple and comparatively inexpensive,

Machinery

Fig. 2. Fixture for Holding Bevel-gear Blanks of Various Sizes

yet it is adapted for use on four pieces of work of different sizes
and the changes required are of such a nature that they may
be performed quickly so that there is very little loss of time.
It may futher be noted that the boring tool is the same in

248 JIG DESIGN

each case and that the adjustment for different diameters is
obtained by the cross sliding movement of the turret.

Adjustable Fixture for Special Bevel-gear Blanks. — The
work A shown in Fig. 2 is a special bevel-gear blank, and these
gears are used in a great number of sizes on textile machinery.
The pieces were held in the first setting by the interior and were
machined on the side having the beveled surface and on the
periphery; they were also partially under-cut along the edge
of the rim in order to provide a clamping surface during the
second setting. Extreme accuracy was required in the work,
and yet there were so many sizes to be handled that the con-
struction of separate fixtures was deemed inadvisable. A
special faceplate B was, therefore, designed having three radial
dovetail slots C (upper view) in its face; and a small portion F
of each of these slots was left straight to assist in locating the
movable jaws D. These jaws were made of steel and were
radially adjustable to various diameters, being clamped in any
desired position by means of the screws G and the dovetail
shoes E. A number of sets of soft steel supplementary jaws H
were drawn back into a seat on the main jaws by the two screws
J and were bored in place to the diameter of the outside of
the gear, the main jaws being set in place to an approximation
of the correct diameter in each instance.

The clamps K were drawn down upon the finished portion
of the work by means of the screws L in the jaws. A bushing
M was set in the center of the faceplate and used as a guide
for the pilot N of the boring-bar P which was held in the
turret. The tool 0 was used to bore the hole while the tool Q
faced the unfinished portion of the gear blank, the latter tool
being held in two toolposts R on the cut-off slide. In handling
some of the larger gear blanks, a supplementary head T (lower
view) was placed on the end of the boring-bar and held in place
by the screws U on the flatted portion of the bar. This head
gave good support to the tool 5 which was used for boring the
larger sizes of gear blanks. This tool was held in place by the
screws X and V, the latter passing through the hole provided
for it in the bar. Fine adjustments were provided for in the

ADJUSTABLE FIXTURES

249

backing-up screw W and the facing of the blank was accom-
plished by the same tool. This fixture took care of seven gear
blanks of various sizes and gave very satisfactory results.

Adjustable Fixture with Means of Maintaining Accuracy. -
A fixture which is somewhat out of the ordinary and which
may be adjusted to handle several sizes of work A is shown
in Fig. 3. As absolute concentricity is required in the finished
surfaces of the work machined in this fixture, it is essential for
the fixture to be arranged in such a way that it can be trued
up if it becomes inaccurate through misuse or neglect. The

Fig. 3. Fixture in which Provision is made to Compensate for Inaccuracy
resulting from Misuse or Neglect

cast-iron nose-piece J is screwed to the spindle in the usual
manner and the supplementary casting H is bolted to it with
the four bolts L. The holes in this piece are slightly larger
than the bolts so that small adjustments may be made. The
flanged portion of the supplementary casting carries four head-
less set-screws at M , by means of which the ring can be trued
up, and check-nuts are provided to secure a permanent setting
of the fixture. The locating rings C are made in several sizes
to take the various pieces that are machined in this fixture,
and each of these rings is furnished with a driving pin D which
enters one of the bolt holes in the work.

250

JIG DESIGN

Machinery

Fig. 4. Simple Fixture for Holding Three Sizes of Steel Flanges, while
boring, facing, and cutting Packing Grooves

The screws N are set into the ring from the rear and are
located in different places for the various rings. The fixture
has three T-slots G in order that the clamps E may be con-
veniently adjustable by means of the T-bolts F which enter

ADJUSTABLE FIXTURES 251

these slots. The boring and shoulder work performed on the
piece is accomplished by the shovel-nosed tool O which is
mounted in the tool-holder P on the turret. This is an example
of a fixture designed for standard work of various sizes coming
through in small lots, and which requires extreme accuracy in
machining. The fixture is a compact design and it is built
close in to the spindle so that, although the fixture itself is
heavy, there is so little overhang that the weight is of small
importance.

Adjustable Fixtures for the Vertical Boring Mill. — The
table of a vertical boring mill is so arranged that it may be
used either as a faceplate or as a chuck with provision for clamp-
ing in the T-slots when necessary. This is a distinct advantage
in many kinds of work and especially so where a number of
pieces of similar construction and different sizes are to be
handled. Fig. 4 shows a simple fixture for handling three sizes
of steel flanges A. The base C of the fixture is made of cast
iron and is centered by a plug D in the table hole; and it is
fastened down to the table by means of the screws F which enter
shoes in the T-slots. In the upper illustration, the work A has
been previously turned, faced and partially under-cut to pro-
vide for clamping, and it is held during the first setting by
means of jaws on the inside of the flange.

On the second setting (shown in the upper illustration) the
operations performed consist of boring the hole, facing the
flange as far as the clamps, and cutting the packing grooves 0.
The locating ring B is slipped on the finished portion of the
base and is drawn down by the screws E. The clamps H are
supported at the outer end by the wooden blocks K, and are
drawn down upon the work by nuts and washers / through
the medium of the T-bolts G which are adjustable radially in
the table slots. The boring-bar L is used for boring the interior
of the flange with the tool M, while the side head (not shown)
faces the flange and cuts the packing groove. The lower illus-
tration shows the fixture adapted for holding the largest piece
Q which it handles. In this case, the ring N is made of some-
what different shape so that it will locate properly on the

252

JIG DESIGN

Machinery

Fig. 5.

Method of holding Three Sizes of Work which has been bored
and faced and has had the Holes drilled in Flange

finished portion of the base C. All other portions of the fixture
are the same as in the preceding instance, the clamps H being
moved outward in the T-slots a sufficient amount to take care
of the work of larger diameter. The tools for boring, facing,
and cutting the packing grooves P are also the same.

ADJUSTABLE FIXTURES 253

Fixture with Adjustable Driver and Soft Internal Jaws. —

The work A shown in Fig. 5 is made in three sizes, the largest
of which is illustrated. These pieces have been previously
bored and faced, and the flange holes have been drilled in a jig.
The base / of the fixture is made of cast iron and is centered
on the table by means of the plug K. It is held down by three
screws G which enter shoes H in the table T-slots, and it should
be noticed that the slots in the fixture permit the T-slots L to
be moved inward to take care of work of smaller diameters.
It is obvious that the screws G must either be moved inward
when ,this is done, or else they can be placed at the extreme
inner position and kept there at all times. The driving pin E
is also arranged in a T-slot cut in the fixture, so that it can be
moved radially to a position corresponding with the bolt holes;
and the shoe F makes it secure in whatever position it may be
placed.

Instead of using a locating ring, three soft jaws B are set
in slots in the fixture base, and these may be clamped in place
by means of the screws C which draw up on the shoes D in
the T-slots. After clamping them in an approximately correct
position, they are turned to the size of the interior of the cast-
ing. Attention is called to the fact that the outside portion of
the hub in the base casting / is finished in order to facilitate
calipering when turning the jaws. The clamps N are supported
at their outer end by wooden blocks O and are drawn down
on the flanged portion of the work by the nuts M. Radial ad-
justment of the clamps is obtained in the manner previously
mentioned. The tools Q and P in the tool-holder R and the
side head, respectively, are used for facing and turning the out-
side diameter of the work. Adjustments for diameters are obvi-
ously obtained by setting the machine slide. This fixture may be
made up at little cost, is easily adjustable and will take care of
a great range of sizes. In addition to this, the accuracy obtained
by its use leaves nothing to be desired.

Adjustable Fixture for a Cast-iron Bracket. — The work A
shown in Fig. 6 is a cast-iron bracket which has previously
been machined along the face D and has had the tongued por-

254

JIG DESIGN

tion cut approximately central with the cored hole at F. Four
holes have also been jig-drilled at /. Two sizes of these brackets
were made several times each year in lots of ten or twelve, so
that the expense of a complete fixture for machining each piece

Machinery

Fig. 6. Inexpensive Fixture for Holding Two Sizes of Brackets

would have been excessive in view of the number of pieces
produced. The following equipment proved satisfactory: An
angle-plate B is tongued on the under side F to fit one of the
table T-slots and is held down by screws (not shown). The

ADJUSTABLE FIXTURES

255

distance E for the two sizes of brackets is easily determined by
placing a stud G in the center hole of the table and locating
the angle-plate B from it. The bracket is placed in position
on the angle-plate so that the tongue H fits into the groove,

Machinery

Fig. 7. Adjustable Fixture for Holding Three Sizes of Bronze
Worm-gear Sectors

and the bolts / are passed through the holes in the bracket and
tightened by the nuts at K.

A little freedom is allowed in the bolt holes and the finished
edge of the bracket rests on the pins C. Two special jaws Q are

256 JIG DESIGN

fixed in position on the table but may be adjusted radially
when necessary to bring them into the correct position for the
other size of bracket. The jaws are provided with set-screws O
which are adjusted to support the overhanging end of the
bracket, after which they are locked by the check-nuts at P.
The jaws are keyed at 5 to the sub- jaws of the table; and the
clamps N are used on the unfinished portion of the bracket,
being tightened by the nuts at R so that the surface to be ma-
chined is clear of interferences. The boring-bar L is used to
bore the hole and the side-head tool M faces the pad. This is
another example of a table being used with a faceplate having
adjustable moving parts on it.

Adjustable Fixture for a Bronze Worm-gear Sector. — The
fixture shown in Fig. 7 was designed to handle three sizes of
the bronze worm-gear sectors A. The base B of the fixture is
centered on the table by means of the stud G in the center
hole, and it is clamped securely by means of three screws P
which enter shoes in the table T-slots. An adjustable V-block
C is mounted on a finished pad and tongued on the under side
to fit the slot D. All the jaws on the table chuck are removed
and a special jaw K is substituted for one of them. This jaw
is slightly under-cut on its face to assist in holding down the
work, and at the same time it forces the hub of the casting up
into the vee locating block. A slot 0 is cut in the base of the
fixture in order to allow the necessary movement for this jaw.
The hub rests on a headless set-screw H which is tapped into
the base, and two other adjusting screws are provided at /.
These are adjusted by means of a wrench after the jaw has been
tightened. The set-screw H, however, remains set after it has
been adjusted to suit the particular piece which is being ma-
chined. A driving screw at L takes the thrust of the cut and
may be removed and placed in either of the holes M or N when
used for the other pieces. In setting the V-block for another
diameter of hub, it is only necessary to loosen the screws F
and move the block radially to the desired position. The jaw K
is readily set to size while the screws J and L are placed in holes
provided for them.

CHAPTER XI

THE FLOATING PRINCIPLE AS APPLIED TO
FIXTURE WORK

There are many instances in the design and construction of
fixtures for machine tool equipment work that require applica-
tion of the floating principle in order to make them thoroughly
efficient. When thin castings are to be handled, the application
frequently takes the form of a system of floating clamps, which
are arranged in such a way that pressure sufficient to hold the
work can be applied without danger of distorting it. It may
also be necessary to have the locating points so designed that
they too will float to a certain extent so as to adapt themselves
to varying conditions. The latter application may be necessary
when rough castings are to be machined, so that inequalities in
the work will not affect the location in the jig or fixture. Ab-
normal or extraordinary conditions sometimes require the ap-
plication of the floating principle to the location of work which
has two or more finished surfaces in different planes.

The nature of the castings for which the fixtures are designed
has a strong influence on their construction, and the type of
machine tools on which they are to be used is also a prominent
factor in the design. The accuracy required in the finished
product, and the number of pieces to be machined, must also
be considered in connection with the design.

Fixtures of this kind may be adapted for work on various
kinds of machine tools, such as drill presses, milling machines,
lathes (turret and engine types), boring mills, or grinding ma-
chines. All of these require fixtures of somewhat different con-
struction, according to the machines on which they are to be
used, and the purpose for which they are intended.

It is practically impossible to cite examples of every kind of
device to which the floating principle can be applied, but typical

258 JIG DESIGN

designs will be described so that the various devices shown
may be applied to a wide range of work.

It is well to state that in connection with the application of
the floating principle, the greatest care must be used in the
design in order to make sure that it is correctly applied, as
it is quite possible to obtain a " float" in some portion of a
device or tool, which, being of faulty construction, will not
produce the results desired.

Important Points in the Application of the Floating Principle.
- In order to obtain the most satisfactory results in its applica-
tion, a few points are here noted which are worthy of attention.

1. As applied to clamping or holding methods, the greatest
care must be used in order to make sure that the floating action
is not constrained in any one direction, but will operate equally
well and with uniform pressure on the required area. Fric-
tional resistance may at times be sufficient in cases of this kind
to cause imperfect work by reason of unequal pressures on the
work itself. When the clamping action is applied to a rough
surface, still greater care must be used in this regard, and the
amount of float must be so proportioned that it will take care
of a considerable variation in the castings or forgings. When a
great number of pieces are to be handled, several patterns are
often used and these will be found to vary somewhat so that
there are slight differences in the resulting castings. For this
reason, due allowance must be made.

2. When applied to methods of locating the work, or as
supporting points on which it rests, the construction must be
such that it will not by any possibility cause distortion. If
springs are used under supporting plugs which are afterward
to be locked in position, the springs must be proportioned so
that they will not be strong enough to cause any trouble by
forcing the piece out of its true position. Also when supports
are placed against finished surfaces they should be so arranged
that they will not injure them. In locating a piece of work from
two previously machined surfaces which are in different planes,
the float-action must be very carefully studied, so that the con-
tacts are positively assured, and no tilting of the work will

THE FLOATING PRINCIPLE

259

result. There are occasional instances which require the loca-
tion of a piece of work from a previously machined surface, in
connection with a threaded portion by which it must be clamped.
In a case of this kind, the "float" must be made so that it will

Machinery

Fig. 1. Piston Drill Jig having Floating Clamps

take care of a possible lack of concentricity between the thread
and the other finished surfaces and at the same time provide
means of equalizing variations in the alignment of the thread.
3. Locking devices for floating members must be so ar-
ranged that the members can be positively locked or clamped
without causing any change in their positions. A turning

260 JIG DESIGN

action such as might be caused by the end of a screw against
a locating point is often sufficient to throw the work out of its
correct position. The interposing of shoes between screws and
floating members will prevent any trouble of this kind.

Other points in construction and design will be noted in
connection with the examples to be described.

Piston Drill Jig with Floating Clamps. — A very good ex-
ample of a drill jig which is provided with a floating clamp to
work on a rough surface is shown in Fig. i, the work being a
piston casting A which has been previously machined at B.
The body of the jig G is of semi-box section and is provided with
feet D on which it may be rested, both during the loading and
when under the drill. A hardened and ground steel stud E is
let into the casting at one end and serves as a locating point for
the machined interior of the piston B. A stud C is further pro-
vided to give the correct location to the wrist-pin bosses.

As the end of the piston is of spherical shape and in the rough
state also, it is necessary to provide a means of clamping which
will so adjust itself to the inequalities of the casting that an
equal pressure will be obtained so that there will be no tendency
to tilt the work. A heavy latch M is pivoted on the pin L and
is slotted at the other end to allow the passage of the thumb-
screw N which is used to clamp it in position. A special screw
0 is threaded into the latch, and is ball-ended at P so that it
has a spherical bearing against the floating clamp Q. The
screw 6* keeps it in position, but it will be noted that clearance
is provided to allow for the floating movement around the body
of the screw. Three pins R are set 120 degrees apart in the
face of the floating clamp so that a firm three-point bearing is
assured. In order to assist in supporting the work under the
pressure of the drill, two spring-pins T are provided, these
being set in the form of a vee near the front end of the piston.
They are encased in a screw bushing U and are locked in posi-
tion by means of set-screws, not shown, after they have been
allowed to spring up against the piston casting. (In order to
avoid confusion in the drawing, one of these pins is shown at
an angle of 45 degrees from its actual position.)

THE FLOATING PRINCIPLE

261

The steel liner bushings F are provided in the body of the
casting so that the main bushings, which are of the removable
type as shown at H} may not produce too much wear in the
jig body itself. A slot is provided in the head of the bushing
so that the pin K will prevent it from turning under the twist-

SECTION W-X-Y-Z

Machinery

Fig. 2. Drill Jig for Rough Steel Collar

ing action of the drill. It should be noted that in the con-
struction of the spring-pins which are used to help support
the casting, the springs themselves should be very light so
that they will not force the piston out of its true position, de-
termined by the locating stud.

Drill Jig for a Rough Collar. — The steel adjusting collar A
which is shown in Fig. 2 has been previously bored, but no

262 JIG DESIGN

other work has been done upon it, the sides being left in their
natural forged shape. Six holes are to be drilled around the
rim, as shown at N, and it will be seen that some care is neces-
sary in the locating and clamping arrangements so that the
resulting holes will be parallel with the axis of the collar. The
jig body C is of cast iron, and is provided with a hardened and
ground steel locating collar B on which the previously machined
interior of the ring is located. The ring is placed on this steel
collar resting against the single steel bushing D which is inserted
in the body of the jig. Two other bushings E are arranged
1 20 degrees apart, and are provided with very light coil springs
which force them up against the under side of the ring. The
shoes F are then set up against the angular cut on these bushings
by means of the screws H. The small set-screws G bear against
the flattened side of the shoes and prevent them from turning.
It will be noted that the angular cut on the body of the bushings
is such as to prevent them from pushing down under the pres-
sure of the drill.

The bushing plate / is located on the stud Q and is prevented
from turning by the pin K which fits the slot L in the body of
the jig. Six bushings N are set into the plate at equal intervals.
A nut P and a C-washer O provide for ready removal of the
plate and draw it down solidly on the top of the locating ring B.
The three pointed screws M are set into the work slightly to
prevent any change in its location. It is well to note that it
would have cost no more to machine one side of the work while
it was being bored, thus obviating the necessity of the floating
locating bushings.

Drill Jig with Floating Bushings and Locating Vees. — A
somewhat peculiar condition is shown in Fig. 3, the work A
being a bellcrank of ordinary construction such as is used in
large quantities in automobile work. There are some instances
on work of this kind when a variation of A inch or more in
the center-to-center distances is not considered of extreme
importance, but it is quite important to have the holes as near
the center of the bosses as possible. In order to counteract
variations in the castings and still obtain holes which are central

THE FLOATING PRINCIPLE

263

on the bosses, it was necessary to adopt some sort of floating
construction such as that shown in the illustration. A number
of jigs of this kind are in use in a large automobile factory and
their action is very satisfactory. In the instance shown the
work is located on a stud / from the previously reamed hole in
the hub. It should also be noted that both hubs and bosses
have been faced to size previous to the drilling operation. A

Machinery

Fig. 3. Drill Jig with Floating Bushings and Locating Vees

sliding V-block Q is carefully fitted to the slot E in the body
of the jig, and on it is mounted the bushing plate P in which
the bushing D is carried. After the piece has been placed in
position the sliding block is pushed forward by the operator
until the vee C comes up against the boss on the casting and
locates it. The thumb-screw F locks the block firmly in po-
sition, and the sliding clamp G holds the work. Another
block S is also cut out in the form of a vee at L, but is not

17 J

264

JIG DESIGN

tongued on its lower side to fit a slot, as in the other instance.
A bushing, plate R is mounted on it with a bushing K at the
forward end. The under side of the block has two narrow
bearing surfaces N and M and it is free to swivel in any direc-
tion required by the slightly varying positions of the boss.

Machinery

Fig. 4. Milling Fixture with Floating Clamps and Locator

The thumb-screw O holds it in place after it has been located
by the operator. The other clamp H is then used to hold the
piece firmly. A drill jig of this kind is not suited to all classes
of work, but it proved satisfactory in this case; the floating
action gives excellent results when absolute accuracy in the
product is not required.

THE FLOATING PRINCIPLE 265

Milling Fixture with Floating Clamps and Locator. — In

the design of milling fixtures a point which is of extreme im-
portance is that of so arranging the various clamping devices
that they will not produce undue strain or distortion. In addi-
tion to this, all members used must be of sufficiently heavy
construction to avoid chatter. The work A as illustrated in
Fig. 4 has been previously chucked and it is desired to mill the
slot H at its upper end in a certain relation to the reamed hole.
The two portions of the casting / and K are left rough, and as
a consequence it becomes necessary to arrange the clamps and
locating points so that they will equalize the inequalities of
the casting. The body of the fixture B is cast iron and of some-
what heavy section, being tongued at its lower side to fit the
slot in the table and held down in the usual manner by the
T-bolts C at each end. The work is placed on the adjustable
plunger D which is pulled back by the pin T passing through
the outer end. A stop collar F is forced on the end of the
shank E in order to prevent too great a movement of the
plunger. The upper end of the work is swung over against
the stop-screw G which is set in a boss in the rib O that ties
the two sides of the fixture together. One of the rough sides K
of the casting strikes against the rocker M which automatically
adjusts itself to the variation in the casting. It will be noted
that the fixture is bored out radially and slightly under-cut to
fit this rocker, and that it is held in place by the screws N.
The holes which these screws enter are slightly enlarged to
permit the necessary movement. Two steel pins U bear
against the other side of the rough casting, these pins being
set in swinging floating clamp Q, the provision for float being
supplied by an over-sized hole at R. The set-screw S bears
against the center of this rocking clamp and gives the pres-
sure necessary to hold the work. A small coil spring throws
the clamp back out of the way when assembling or dissembling
the work. The direction of the cut in machining the slot is
such that the pressure comes against the solid body of the cast-
ing and not against the clamp. Clamping members which
float are found on various designs of fixtures.

266

THE FLOATING PRINCIPLE 267

Locating Device with Floating Pressure Compensator. -

The work A, shown in Fig. 5, has been partially machined in
a previous operation, and the flange has also been drilled so
that one of the holes can be used for driving purposes. The
machine to which this device is applied is a turret lathe of
the horizontal type, and the body B is screwed to the spindle
end C in the usual manner. The pin T is set into a boss in
the face of the fixture and acts as a driver in one of the flange
holes. Two steel rings F and G act as approximate locators
for the work when it is first placed on the fixture. Two cy-
lindrical steel cams H and / are accurately ground to fit the
central hole in the fixture, and are operated by the rod M
which is threaded right- and left-hand, respectively, at N and
O. Each cam is milled to a 20-degree angle at K and L, three
of these slots being equally spaced around the periphery so
that their angular surfaces control the movement of the locat-
ing pins D and E. The coil springs return the pins to an in-
active position when released by the cams. A plug P is placed
in the spindle as shown in the illustration, for the purpose of
providing a seat for the coil spring Q which assists in the re-
leasing of the pins after the machining has been done. The
two stop-pins R and S limit the movement of the cams and
take all the thrust of the twisting action of the operating
screw.

In this connection it is well to note that these stop-pins are
a nice fit in the cam slots, while the locating pins have a side
clearance in the angular slots of o.oio inch so that there is no
possibility of trouble being caused by friction at these points.
Attention is further called to the fact that the action of the
cams is such that a true floating motion is produced when the
screw is operated so that all of the locating pins are set up
with an equal amount of pressure. A floating action of this
nature may be readily applied to holding fixtures for a great
variety of work.

Chucking Fixture with Floating Clamps and Taper Locating
Plug. — A somewhat unusual condition is shown in Fig. 6,
the work A being a special clutch flywheel which has been

268

THE FLOATING PRINCIPLE 269

partially machined. In order to obtain concentricity of the
various surfaces, it is necessary to locate the work from the
taper in the hub. In order to compensate for slight variations
between the taper and other finished surfaces, a tapered shell
locating bushing B is centrally located on the stud C which is
held in place in the faceplate fixture E by the nut and washer
at D. A light coil spring M insures a perfect contact with the
tapered surfaces, while a small pin N restrains the movement.
As the outside of the work is to be finished during this setting,
it is necessary to grip the casting in such a way that the clamps
will not interfere with the cutting tools, nor cause distortion
in the piece itself. With this end in view, the three lugs around
the rim of the fixture are provided with shell bushings K, each
of which is squared up at its inner end to form a jaw which is
bored to a radius corresponding with the rim of the casting L.
It is splined to receive a teat screw / which prevents it from
turning, and it also gets a good bearing directly under the point
where the work is held so that there is no danger of springing
out of shape.

The bolts F pass through the shell bushings and are furnished
with nuts G at their outer ends, the nuts having a knurled
portion O which permits of rapid finger adjustment before the
final tightening with a wrench. It will be seen that this con-
struction automatically obtains a metal-to-metal contact with
the thin flange of the casting without distorting it in the least,
as the floating action of the bushings equalizes all variations
and yet holds the work very firmly. After the clamps have
been set up tightly, they are locked in position by the set-
screws H at the rear of the fixture. This application of the
floating principle may be adapted to many kinds of work,
and the results obtained leave nothing to be desired. The
machine for which this device was designed is a turret lathe
of the horizontal type.

Two-jaw Chuck arranged with a Floating Jaw. — The work A,
shown in Fig. 7, is a motorcycle flywheel which it was desired
to machine in one setting complete. The machine to which
the equipment was applied was a horizontal turret lathe. Several

270

JIG DESIGN

lugs on the interior of the casting prevented the work from be-
ing held in a three-jaw chuck, on account of interferences with
the jaws. A two-jaw chuck was, therefore, utilized, and inter-
ferences thereby avoided. As the centering action of a chuck
of this type is very uncertain when used for holding work by
an interior surface of comparatively large diameter, some method
of locating was necessary which would at the same time center
the casting, and yet not cause trouble by interfering with the
lugs on the interior of the flywheel. (The lugs on the interior
of the casting are not shown in the illustration, in order to
avoid confusion.)

The chuck body B is screwed to the spindle C in the usual

Fig. 7. Two-jawed Chuck arranged with a Floating Jaw

manner and is provided with two special jaws, one of which, E,
is of plain design having two bearing surfaces on the inner rim
of the flywheel casting. The other, D, is grooved to fit the
chuck like the regular jaw, but is very much wider as it comes
above the face of the chuck. This portion is turned to a radius
at H and given an angle of 10 degrees at the same time in order
to counteract the lifting tendency which might cause trouble
when the jaws were tightened. The floating member or ' l rocker ' '
F is mounted on this jaw as shown in the illustration, and is
limited in its movement by the two screws G and the elongated
holes in the rocker. This construction gives a very good center-

THE FLOATING PRINCIPLE

271

Machinery

Fig. 8. Piston Chuck having Floating Clamping Features

272 JIG DESIGN

ing action, and the rocker jaw has sufficient "float" to take
care of variations in the casting.

Piston Chuck having Floating Clamping Features. — The
work A, shown in Fig. 8, is a large automobile piston which
has been bored and faced on the open end to a predetermined
size and which is to be completed in this setting, concentric
and square with the finished portion. Previous to this setting
and after the boring and facing operation, the wrist-pin hole
is rough-drilled in a jig in order to facilitate the holding of the
work on the fixture.

The casting is located on a hardened and ground steel ring
F which is forced on the body of the fixture B, and a small
annular groove on the ring prevents trouble or errors in lo-
cating, which might be caused by the presence of chips or dirt
on the locating surface. The body of the fixture is held in
place on the table of the machine by the bolts C which enter
the table T-slots, and it is centered on the table by the plug D
which is forced into it at S. The clamping pin L is ball-ended,
and has a spherical portion in the center also. It is slotted
at N so that the pin M in the draw-bar G will enter the slot
as it is passed through the wrist-pin holes, and bring up against
the shoulder so as to center the clamping pin in the piston. A
great deal of strain is taken by this clamping pin, and for this
reason it is made of tool steel and spring tempered, so that
there will be less chance of breakage.

The draw-bar G is also of tool steel, and it is keyed with a
Woodruff key at H to prevent its turning, the key being a
sliding fit in the body of the fixture. The lower end of the rod
is threaded with a 4-pitch Acme thread, double, left-hand,
to fit the operating nut Q, this latter being provided with a
handle R which extends out through a cored opening O in
the fixture. The permissible movement of this handle is suf-
ficient to produce a vertical movement of A inch of the draw-
bar, which is ample for the purpose of clamping and releasing.
A thrust collar P is interposed between the operating nut and
the boss on the under side of the fixture, and a coil spring J
keeps the rod up so that the clamping pin may be easily placed

THE FLOATING PRINCIPLE

273

WORK A

Machinery

Fig. 9. Chuck Jaws with Floating Locating Points

in position. The pocket E in the upper end of the centering
plug is for clearance only. A heavy pin K acts as a driver
against one of the wrist-pin bosses, so that the draw-rod and
pin are not called upon to perform this part of the work.

While this chucking device is very rapid in its operation,
there is no tendency to tilt the piston or distort it in any way,

274

JIG DESIGN

as the floating action of the pin with its three-point bearing
equalizes all pressures, and at the same time provides a very
secure method of clamping the work.

Chuck Jaws with Floating Locating Points. — The work A,
shown in Fig. 9, is to be bored, shouldered and faced complete
in one setting, and on account of its length it was considered
necessary to provide additional supporting points besides the
jaw surfaces. A set of special jaws B is keyed to the sub-jaws
in the table at D, each special jaw being shouldered at C to
support the work.

The brackets E are tongued at F to fit the special jaws and
are secured thereto by the screws G. These brackets act as a

Machinery

Fig. 10. Grinding Fixture for Steel Collars

support for the steel floating ring M in which the three spring-
pins / are placed. Elongated holes at points N allow the
required floating action, the ring being clamped by the collar-
head screws. The brackets on which the ring rests are pro-
vided with a shelf H which is offset slightly from the center
so as to give the necessary width for the screws. In using the
device, the screws L and N are loosened, and the work placed
in the jaws, which are then tightened while the ring floats
sufficiently to allow for variations. It will be noted that the
pins, being spring-controlled, adapt themselves to the casting
and are there locked by the screws L, after which the ring itself
is clamped by the collar-head screws N.

THE FLOATING PRINCIPLE 275

Although the floating action of this device was satisfactory,
the driving or gripping power was found insufficient to hold
the work securely, and it became necessary to replace the
spring-pins with square-head set-screws, cup-pointed, the ring
being tapped out to receive them. The ring was then allowed
to float while these screws were lightly set up on the work
after which the clamping screws N were tightened. After this
change in construction, the action of the mechanism was much
improved, and the driving power was found sufficient.

Floating Clamping Ring on Grinding Fixture. — The work A
shown in Fig. 10, is a steel casting which is to be ground on
the two exterior surfaces. A nose-piece D is screwed to the
end of the spindle E and is provided with a hardened and ground
locating ring B on which the work locates. The stud C is forced
into the nose-piece and is threaded on its outer end to receive
a spherical nut F. The collar G is concaved to the same radius
as the spherical portion of the nut so that it floats against the
end of the work.

CHAPTER XII

APPLICATION OF THE THREE-POINT PRINCIPLE
IN FIXTURES

The three-point principle is illustrated by a stool having
three legs. Such a stool will be firmly supported even when
placed upon an uneven surface, which is not the case if a stool
having four legs is used. If a jig having four feet is placed
upon the table of a machine, and there is a chip under one of
the feet, this will cause the jig to rock when pressure is applied
to the upper side; but if there were only three feet and these
were located with one foot on a line mid-way between the two
feet at the opposite end of the jig, a chip under one foot would
not cause a rocking movement. The jig, however, would be
tilted upward and, as explained in Chapter I, this might not
be noticed by the operator. For this reason, four feet are
generally considered preferable when they simply serve to
support the jig or fixture. In the mechanical field, however,
the principle of three-point support is applicable to many
classes of work and its importance is understood and made use
of in various kinds of machine and fixture work. In the auto-
mobile industry, alignment of the working parts is preserved
by making the power plant a self-contained unit and having
it supported on three points in order to equalize or neutralize
the twisting action caused by the passage of the car over the
more or less uneven surface of the road. If some provision of
this kind were not made, distortion of the parts would result
and they would consequently fail to operate properly.

In machine design, the three-point principle is utilized in
numerous ways. Sometimes the bed of a lathe is supported
on two points at one end of the machine while the other has
a single swivel bearing or its equivalent. The machines pro-
vided with this feature are easily set up without danger of

276

THREE-POINT PRINCIPLE 277

distortion or changes in the alignment. Some other types of
machine tools also have a three-point support and this principle
is applied to machine design in various ways to secure a solid
support, to equalize strains, etc. Castings for various purposes
are often made with three projecting lugs or bosses in order
to gain a good bearing surface under all conditions. In the
design of fixtures, the principle of three-point support is used
in many ways, on both rough and finished work and on all
varieties of machines. In this chapter we shall consider its
application to fixtures for horizontal and vertical turret lathe
work, and in order to make the matter as clear as possible,
simple examples have been selected to illustrate the subject
and to avoid complications.

Three-point Locating and Clamping Devices. — In applying
the three-point principle for the location and support of rough
castings or forgings, there are several important points to
consider. To begin with, it is well to make sure that none of
the points will strike against a fin or parting seam, or come
against the portion of the work on which the piece number may
be imprinted. If the work is to be located from two rough
surfaces at right angles to each other, it must be remembered
that, if three fixed points are used as locators on one side, the
other points must be arranged so that only one is fixed, and two
are adjustable to compensate for variations in the surfaces.
When the work is shallow and is held in chuck jaws, this point
may be neglected, as the work can rest on three points and
be gripped by the jaws.

When a finished surface is used for centering a piece in a
fixture, and it also rests on a finished surface, the three sup-
porting points may be fixed. If the work is to be clamped as
on a faceplate fixture, the clamps should be arranged so that
they will draw the piece directly down or back upon the sup-
ports in order to avoid any chance of tilting or distortion.
When a finished surface is used for centering the work and a
rough one for end location, the points must be arranged the
same as for handling rough castings, i.e., with two of them
adjustable. It is often desirable on large work to locate the

278 JIG DESIGN

piece on three strips instead of on a continuous surface in order
to facilitate assembling. When this is necessary, it is advisable
to make the strips in such a way that they can be readily
replaced when worn.

The supporting points should be so located that they can
be easily reached for cleaning, in order that locations will not
be affected by an accumulation of chips or dirt at important
points. Adjustable points should be so arranged that dirt and
chips will not clog the screws and thus make them difficult to
operate. This point in design should receive careful attention
when fixtures are designed for use on the vertical turret lathe
or vertical boring mill. On machines of the horizontal type,
less trouble is likely to be experienced in this respect, because
the chips do not tend to fall on the screws. In either case,
however, it is always well to provide against any trouble from
this source.

It is frequently desirable to insert hardened steel buttons of
uniform height in the jaw screw holes in order to raise a portion
of the work above the tops of the standard jaws, so that the
work can be faced or under-cut. These buttons form an excel-
lent three-point support for the work in addition to performing
the function already mentioned. Short parallels cut from cold-
rolled steel may be used on a vertical turret lathe and are
somewhat cheaper than the buttons, but they are open to the
objection of becoming easily displaced and lost.

When it is necessary to arrange points to act as a vee on long
cylindrical surfaces, it is good practice to make them so that
they can be adjusted to take up wear. This can easily be done
by means of headless set-screws with check-nuts to lock them
securely in any position; and it is a better construction to
place one check-nut on the outside and another one inside,
than to have both nuts on one side of the fixture wall. The
construction of the fixture will not always permit of using this
method, but, when it will, very satisfactory results are obtained.

When the three-point support is applied to the fixture itself,
the clamp screws which hold the fixture in place on the table
should be arranged at the points where the supports are placed,

THREE-POINT PRINCIPLE

279

Machinery

Fig. 1. Application of Three-point Principle in holding a Flywheel while
performing Boring and Facing Operations

and any clamps for the work itself should be as near the same
place as possible.

Three-point Support for Flywheel Fixture. — The fixture
for the motor flywheel shown at A in the upper part of Fig. i
has a three-point support. The flywheel is of such a diameter
that a single supporting point in one of the chuck jaws would

280 JIG DESIGN

not be sufficient to resist the pressure of the cutting action of
the various tools used in machining. The work is held by the
inside in the special jaws B which are relieved at E to permit
the back-facing of the rim. The tools L and K, which are held
in a special tool-block on the cut-off slide, are used for back-
facing and finishing the pad; and other tools (not shown) in
the turret face the portion W of the flywheel. The boring-
bar / has a pilot H which enters the guide bushing G in the
chuck to give greater accuracy and rigidity. Two of the jaws
are provided with spring-pins C which are released and locked
by the action of the screws F on the shoes D. The stop-pin in
the third jaw is fixed in order to give positive longitudinal loca-
tion of the work. Work of this kind is very frequently located
on the three fixed ends of the jaws and gripped by the inside
as shown, but when this is done there is always a chance of
incorrect holding and possible slippage due to spring of the
casting. Sometimes this results in the production of grooves
or a wavy surface on the outside of the work.

In the second setting of the work a fixture is used and the
point of location is the recess which has been machined in the
first setting. This locates the piece on a plug M which is
shouldered at N and fits a hole provided for it in the center of
the fixture. The previously machined surface W rests on three
pins P which are of uniform height and so arranged that they
leave a slight clearance between the face of the plug M and the
face of the shoulder on the work. The fixture body 0 is screwed
to the spindle and its exterior forms a continuous ring S so as
to make this surface clean and avoid danger to the operator
through projecting lugs, etc. The work is drawn back against
the pins P by means of the clamps R through the medium of
the screws Q. Work of this kind is frequently held and drawn
down upon a continuous finished surface instead of a series of
pins. The disadvantage of a continuous surface is that dirt
collects upon it and renders location uncertain unless great
care is taken to keep the fixture clean.

Three-point Fixture for a Pot Casting. — The fixture shown
at H in Fig. 2 was arranged to hold the casting A which is

THREE-POINT PRINCIPLE

281

SECTION X-Y-Z

Machinery

Fig. 2. Three-point Fixture for a Pot Casting

of large size, instead of using jaws, for the reason that better
supporting and driving facilities were required than could be
obtained by means of jaws. Large castings held in a fixture
require considerable clearance between the work and the fix-
ture, because of the variation in size and also on account of the
finish allowance that is necessary. Care must, therefore, be

282 JIG DESIGN

taken to see that the amount of clearance is ample to take
care of any condition which might be found. An inch of clear-
ance all around is none too much on a large casting. The pot
fixture H is centrally located on the table by the plug / and
is fastened down by the T-bolts O in the table slots.

The set- screws at B and C serve as locating points for the
casting. There are two screws at B and one at C, the latter
being located midway vertically between the other two and
90 degrees from them. This is somewhat contrary to the usual
custom and in some cases might not be found desirable — for
example, when considerable dependence has to be placed on
the locating screws to assist in driving the work. In this case,
however, ample provision for driving is obtained. The work is
forced over against points B and C by the central set-screw D
of the three shown. When the casting has been brought up
snugly into place, the upper and lower screws D are also
tightened. Protection against chips is provided for in con-
nection with these set-screws, no portion of the thread E being
exposed. The work rests on a fixed point G (shown in the
upper view) which acts as a positive stop. Two additional
points F are adjustable by means of a wrench, and their threads
are protected from dirt by a cylindrical portion above. The
openings P in the wall of the fixture allow access for the screws;
the U-clamps L draw it down upon the points by means of
the nuts and washers M on the studs K. The clamps L being
of U-section are readily removable without requiring the nuts
and washers to be taken off. The plan view shows only one
clamp in position in order to show this clearly.

Two Methods of Obtaining a Three-point Support on a Hub
Casting. — The work A, shown in the upper portion of Fig. 3,
is a hub casting of large size, and the method to be described
was first suggested in connection with the handling of this work.
The idea was abandoned, however, in favor of the method
shown at the lower part of the illustration. In the upper illus-
tration, the jaws C are mounted on the raising blocks E and
tongued to them at D, while the raising blocks are tongued
and fastened to the sub-jaws of the table at F. Three hardened

THREE-POINT PRINCIPLE

283

points B are set in projections of the upper jaws and the work
rests on these points. A supplementary casting G is centered
on the table by means of the hollow plug M which also acts

Machinery

Fig. 3. Original and Improved Methods of holding Large Hub Casting by
Three-point Support

as a guide for the boring- bar pilot O; and the upper part of
this bushing is beveled as shown, but the edge of the hole is
left sharp so that chips will not be drawn down with the bar
and tend to destroy it together with the bushing. The base of

284 JIG DESIGN

the fixture is slotted at three points H to allow the necessary
movement of the jaws; and there are three lugs midway be-
tween the jaws on the base, in which the spring-pins / are
carried. After the work has been centered by the jaws, these
pins are released and allowed to come into contact with the
work; they are then locked by the set-screws L. The boring-
bar P is of the multiple type, having two tools Q and R for
the two inside diameters. The tool Z is carried in the upper
part of the side head instead of the lower, in order to econo-
mize on the length of the boring-bar.

As the purpose of three supporting points / was simply to
steady the work, it was thought that a simpler design would
answer all purposes, and the previous method was therefore
abandoned in favor of the one shown in the lower part of
Fig. 3. In this case the bushing T is used directly in the center
hole of the table and the boring-bar is made correspondingly
shorter. The raising blocks V are also lower than in the pre-
vious case, and are keyed to the sub-jaws at X in the same
manner. The construction of the jaws C is identical in both
cases. Three spring plungers S with knurled ends W are inserted
in the jaws and tightened in any desired position by the set-screws
U. This method is much simpler than the other and possesses
the added advantages of being both cheaper and more efficient.

Fixture having Three Clamping Jaws and Three Locating
Pads. — The work illustrated at A in Fig. 4 has been partially
bored and faced, and in the setting shown, it is necessary to
work from the previously finished surfaces. The base cast-
ing E is slotted to receive the three steel locating jaws C on
which the finished surface B locates. These jaws are held in
place by the screws D and are carefully finished after being
drawn into position. The base is centered by the plug F in
the table hole G, and is held down by the screws Q in the lugs P,
one of which is shown in the plan view. Three pads H are
finished to support the flange and a driver / is inserted in one
of these pads. The work is clamped by means of the hook-
clamps K in order to keep the diameter of the fixture as small
as possible; and a cap-screw L passes through the hook-clamp

THREE-POINT PRINCIPLE

285

and enters the bushings M into which it is threaded. The
hook-clamp is backed up by the lug R so that it will not be-
come distorted when under strain. The boring-bar N in the

Machinery

Fig. 4. Fixture provided with Three Clamping Jaws and Three
Locating Pads

main-head turret, and the tool 0 in the side head, are indicated
in order to show the method of machining.

Double Three-point Locating Device. — A somewhat peculiar
arrangement is that shown in Fig. 5 for holding a piece of work

286

JIG DESIGN

A by the interior cored surface. The base B is made of cast
iron and is centered on the table by means of the hollow plug C.
It is held down by screws D which enter shoes in the table

Machinery

Fig. 5. Method of holding a Piece of Work by an Interior Cored Surface

T-slots. The upper portion of the fixture E fits a circular
tongue F on the base, to which it is fastened by the screws
G. The upper portion E is slotted to receive the jaws N and 0,

THREE-POINT PRINCIPLE 287

and there are three pairs of jaws set 120 degrees apart. The
upper portion of the fixture E is made separate in order to
facilitate the machining of the slots. Two cylindrical cams H
and / control the radial movements of the jaws by means of
the screw K which is threaded with a coarse-pitch left-hand
thread in the lower cam and a right-hand thread in the upper
cam. The upper end of the rod is squared at L and is operated
by a socket wrench M. In order to prevent the entry of chips
and dirt into the mechanism, a felt washer S is fastened to
the upper cam; and steel cover-plate R is placed on top of
the fixture and held in place by screws. The hardened steel
pin T strikes against the inner cored surface and locates the
piece vertically. Slots are cut in the upper portion of the fix-
ture E to allow the insertion of the flat springs Q which throw
the jaws back into position upon withdrawing them from the
work; and a sheet steel cover-plate P keeps the dirt out of
these slots. The cams and screw are supported by the coil
spring shown below the lower cam, and the action of the cams
is limited by the screws U which enter slots in the cams. These
screws also serve to prevent the revolution of the cams. A
combination boring and reaming bar W is used for boring and
reaming the hole while the outside surfaces are machined by
various tools in the side head, one of these being shown at V.

In the construction of this device it will be noted that al-
though six points or jaws are used for locating, the arrangement
is such that they all bear against the inside of the casting with
an equal amount of pressure, at the same time centering the
work from the cored interior. As the right-and-left screw on
the rod K is rotated, the two cams float vertically so that the
pressure on the jaws is equalized. A device of this kind is
useful in many instances when work is to be held from an internal
cored surface.

CHAPTER XIII

SPECIAL JIG AND FIXTURE MECHANISMS

No single item influences the production rate to as great an
extent as the design of jigs and fixtures. The saving of a few
seconds clamping time means an increased production that off-
sets a high first cost. It is much easier for an operator to clamp
his work by tightening one nut than the usual three, and, aside
from the saving of time, he is expending less energy and works
to better advantage to himself and his employer.

It is usually necessary to equalize the pressure in a jig before

Machinery

Fig. i. Simple way of Clamping a Bushing for Drilling

applying the clamping pressure. When equalizing and clamp-
ing mechanisms are both operated by a single clamping operation,
the danger of clamping before equalizing the pressure can be
eliminated. Many object to the term "fool-proof," but the
amount of work spoiled or sprung by careless clamping justifies
care in designing jigs and fixtures that are at least " error-proof "
in this respect.

The mechanisms described in this chapter are selected for
their suggestive value, and only as much of the fixture is shown as

288

JIG DESIGN

289

is absolutely necessary. Great care should be used in selecting
the mechanism desired, so that it meets the clamping or equaliz-
ing conditions of the work in hand. The examples shown are
in many cases obtained from milling fixture designs, but the
principles apply equally to drill jigs.

As an example in the choice of clamping mechanism, consider
the piece A, Fig. i. It is required to drill the hole B. A simple
way of clamping this piece is illustrated in Fig. i, using a hexagon
nut and washer. The time required for running on and off the
hexagon nut is saved in the design shown in Fig. 2, using a
quarter-turn knob. Stud B has a flat milled on both sides of

MacKlnery

Fig. 2. Using a Quarter-turn Knob for Clamping the Work

its threaded portion. The slot in knob A slides on over this
flat and a quarter turn clamps the work. If the variation in the
length of the work is not too great, this makes a rapid clamping
arrangement.

Fig. 3 shows another means of clamping the same piece, in
which the variation in length of the work and the time required
for turning the knob to match the flat on the stud has been
considered. The slotted washer A and knob B are dropped over
stud C; washer A is held against knob B, which can then be
screwed up as freely as a solid knob. This can be used for a

2 go

JIG DESIGN

variety of bushings of various lengths, the stud C being made to
suit the longest piece of work.

Clamps that have a tendency to draw the work down firmly
onto the rest-pins or stops are useful in all classes of fixtures.
Fig. 4 illustrates a simple means of accomplishing this. Care
should be taken to see that the stop is pivoted above the point A .
Another and more rigid device is illustrated in Fig. 5. The
plunger A, carried in plunger B, is forced down against the 45~de-
gree side of stop C, compressing spring D. A fixture that clamps
two clamps with a " down-and-in " pressure is illustrated in Fig. 6.

JTacMncry

Fig. 3. Means used for Clamping Bushing when the Work
Varies in Length

Slides B are equalized by strap C and ball-and-socket washers
D and E. This fixture is useful for milling and profiling, as the
clamps and stops are below the surface of the work. Fig. 7 shows
two down-and-in clamps equalized for holding a round piece of
bored work for a milling operation. Lever A is tapped to re-
ceive screw B, and the clamping pressure equalizes with lever C
by means of rod D. Levers A and C impart a down-and-in
pressure to plungers E. This fixture can be applied to flat work.
In the double movement clamp shown in Fig. 8, the clamp A is
carried by the hinge B, pivoted at C. Screw E gives clamp A

JIG DESIGN

2QI

a down-and-in movement by means of a 45 -degree taper on stud
D. The stud D is milled off at F to give the clamp sufficient
movement to remove the work. A mechanism for drawing down
both ends of two pieces, by means of a single nut, is illustrated in
Fig. 9. Each piece is clamped independently, thus making it
suitable for use on rough castings or forgings. Rod A, running
through the fixture, carries ball-and-socket washers at each end
and draws the end clamps B and C together. These clamps are
given a down-and-in movement against the 45-degree wedge
ends of rods D and E. The clamping thrust against rods D and
E imparts a downward movement to the inner clamps G and H,

HEIGHT OF PIVOT ABOVE
CLAMPING POINT

Machinery

Fig. 4. Simple means for
Drawing the Work down
Firmly onto the Locating
Pins

Fig. 5. Another Example of
Clamps Drawing the Work
down Firmly onto the Lo-
cating Pins

pulling the work down on the inner rest-pins. The clamps are
returned by means of plungers K and spring /.

The fixture illustrated in Fig. 10 shows a method of drawing
down two clamps and throwing the work against the stop-pin
by a single clamping operation. Tightening nut A clamps down
clamp C and pulls up rod B against the 45-degree tapered end
of rod D, giving a lateral movement against plunger E. Plunger
E is carried by the floating stud G. On the upper end of stud
G is a i5-degree taper that operates against plunger H. Plunger
E imparts, first, an upward movement to floating stud G, which,

292

JIG DESIGN

SECTION A-A

Machinery

Fig. 6. Fixture with Arrangement for Clamping Two Clamps with
a " Down-and-in " Pressure

Machinery

Fig. 7. Fixture having Two Equalizing Clamps

JIG DESIGN

293

in turn, forces out plunger H and throws the work against stop-
pin /; second, a downward pull on plunger K, drawing down
the clamp L. Thus the work is thrown against the stop-pins
before the final clamping pressure is applied. Clamps C and
L are held up by spring plungers, not shown.

The clamping pressure on eight small washers is equalized,
and the washers clamped with a down-and-in movement in the

Machinery

Fig. 8. Another Type of Double Movement Clamp

fixture shown in Fig. n. Rod A clamps the equalizers B and
C, which equalize the pressure against D and E on the one side,
and F and G on the other. Clamps D, E, F, and G are given a
downward pull by four plungers H, which also impart a down-
ward pull on the inner clamps /, K, L, and M . The clamps
are bored to receive the washers, and are returned to a normal
position by the spring plungers N.

2Q4

JIG DESIGN

Fig. 12 illustrates a center clamp that gives a downward and
outward thrust by means of the tapered ends of plate A, which is
carried by plunger B. Plunger C wedges down the plunger Z),
which is tapped into plunger B. Plungers B and D are held up

WORIt

Machinery

Fig. 9. Mechanism for Drawing down Both ends of Two Pieces by
a Single Nut

by a spring E. A small pin in plunger D allows a half turn of
plunger B, so that the work may be lifted out.

In the fixture illustrated in Fig. 14, the work (two clutch shells)
is equalized and clamped by a single movement of the handwheel

Machinery

Fig. 10. Method for Drawing down Two Clamps and Forcing the
Work against the Stop-pin by a Single Clamping Operation

B, drawing out rod C against the collar D. The section A- A
shows how this collar equalizes its thrust with plungers E and
F. The collar D is free to slip to either side as required for
equalizing. The plungers E and F draw in rods G and H through

JIG DESIGN

295

the medium of collars / and K. The strap M, held central by a
small spring and plunger, equalizes the pull on the center clamp.
All clamps are made to clear the work, when it is to be removed,
by means of the lever L and the system of levers shown in the
lower view.

Machinery

Fig. ii. Fixture for Equalizing the Clamping Pressure on Eight
Small Washers

Figs. 13 and 15 illustrate a small double movement clamping
mechanism for hand milling or profiling use. In Fig. 13, the
clamping pressure against clamp A also pulls out plunger B,
throwing up plunger C and throwing the work against stop E,
by means of plunger D. Spring plunger G is used to return
plunger D. In Fig. 15, the pull through clamp A on plunger B

19 j

2Q6

JIG DESIGN

^—^.^ fs/ rJT->| ,N>\

WORK
— — -^..

Machinery

Fig. 12. Center Clamp giving a Downward and Outward Thrust

»=n&J

Machinery

Fig. 13. Small Double Movement Clamping Mechanism for Hand
Milling or Profiling Machines

JIG DESIGN

297

throws the work against the stop C, by means of plungers D
andE.

In profiling or face milling fixtures, clamps on top of the work
often interfere with the cutter. Fig. 16 illustrates a method of

Machinery

Fig. 14. An Equalized Clamping Arrangement making use of a
Hand wheel

holding this class of work by means of a flange at the bottom.
Clamp A is operated by the wing-nut B and floats in slots to
allow for any casting variation, and for hooking the projection
on the clamp over the flange. The piece C is thrown over after

2Q8

JIG DESIGN

the clamp is hooked over the flange. Care must be taken that
the point X is below the pivot point of the piece C.

Fig. 17 illustrates part of a heavy milling fixture for clamping
against the stop-plate A, by means of the two plungers B and
C, by equalizing with the plunger D and sleeve E working against
B and C with 45-degree wedge cuts. Projections on the work
often prevent the use of plain clamps. Fig. 18 shows a resort

Machinery

Fig. 15. Another Double Movement Clamping Mechanism

to an unusual, but efficient, clamp to meet these conditions.
The use of plungers A and B permits the clamp to be operated
from the rear by means of a screw C and knob D. When work
is long in proportion to its width or when the locating pins must
be placed close together, as in the piece illustrated in Fig. 19,
there is danger of it "cocking" or binding between one locating
pin and the screw, if a plain screw is used to throw the work

JIG DESIGN

299

against the locating pins. The use of a roller instead of a screw
prevents this. The roller A will turn until the work strikes
both stop-pins. In the device illustrated, B and C are the fixed
locating pins, and Z>, the clamp screw tapped into the bushing

Machinery

Fig. 16. Clamping Work by Holding it by Means of a Flange

Machinery

Fig. 17. A Heavy Milling Fixture with Equalizing Clamping
Device

E operating the sliding plunger G. It is obvious that the work
can be prevented from binding by using two equalizing plungers
to throw it against the locating pins instead of a roller.

Fig. 20 shows the locating mechanism for a milling fixture in
which two pieces are located by two plungers each, all operated

300

JIG DESIGN

Machinery

Fig. 1 8. Special Type of Clamp used where Projections on the
Work Prevent the use of Plain Clamps

Machinery

Fig. 19. Using a Roller to Prevent Unequal Binding against the
Locating Pins

JIG DESIGN

301

by a single clamping operation. Lever A draws out plunger B and
throws in sleeve C, operating the plungers D and E. Plungers
E are smaller in diameter than plungers D and permit of enough

Machinery

Fig. 20. Locating Mechanism where Two Pieces are Located and
Clamped in a Single Operation

lateral movement to equalize plungers G through the auxiliary
plungers H.

Fig. 21 represents a milling fixture with a quick-release feature.
The particular work illustrated is milling a flat on a small bush-

Fig. 21. Milling Fixture with a Quick-release Feature

ing made on the screw machine. The bushings are held on the
pins A and B and clamped with the eccentric handle C, which
draws in the hinged leaf D. Details of the quick-release lever
are given.

Fig. 22 illustrates half of a fixture for milling a cylindrical

302

JIG DESIGN

concave surface on an unusual piece. The work is clamped
against the pads A and B, on previously milled surfaces, by
means of two differentially operated plungers C and D, similar
to a previously described device. To prevent springing under
cut, the work is backed up with the floating plunger E on the
one side and F and G on the other. The plungers are operated
by push-rods H and /. These push-rods are hand operated and
are clamped by the bushing K and star knob L.

Machinery

Fig. 22. Fixture for Milling a Concave Surface provided with Sliding
Supports under the Milled Surface

Some occasions arise in which the 45 -degree plungers do not
permit of sufficient clamping movement. The mechanism in
Fig. 23 was designed to overcome this objection. An unusually
large movement of the clamp is required to clamp directly over
the rest-pin. Rod A, operated by screw B, imparts movement
to both plungers C and D. Plunger C pulls clamp E down and
plunger D pushes up on clamp E through the plunger G. The
wedge angle between plungers C and D should be less than
that between plungers A and C. There is considerable friction
in this mechanism.

JIG DESIGN

303

Machinery

Fig. 23. Mechanism when an Unusually Large Movement of the
Clamp is Required

F-—

1 |

•^

^, —

Zf^^-~

x ^oil"

/l p

H—

c x

U— ij^

r~ i

— x

/r-f,

Fig. 24. Rigid Mechanism for Clamping at Three Points by
Means of One Screw

A very rigid mechanism for clamping at three points, by means
of one screw, is shown in Fig. 24. In this case, it is shown
applied to a drill jig, but it is rigid enough to permit its use in
milling or planing fixtures. In these cases, the clamping pins

3°4

JIG DESIGN

become rest-pins and are subject to the thrust of the cut. Screw
A thrusts against equalizing plunger B. The details of this
plunger mechanism are illustrated in the engraving. Plunger B
is of less diameter than the drilled hole and rests on the piece C.
This piece is cut from a rod of the same diameter as the hole
and is used to afford a flat base for plunger B to rest on and insure

Machinery

Fig. 25. A Simple Ejecting Device

full contact of the wedge end against the plungers D and E.
Plunger G is a duplicate of B and equalizes the plungers F and H
by means of the same mechanism.

Considerable saving of time may be effected by the use of
ejectors. Fig. 25 is an example of the use of an ejector. Push-
rod A has four notches milled tapering on one end. The pins

JIG DESIGN

305

B are bored and slotted to receive the rods C. These rods are
operated by the wedge cuts in push-rod A. The four pieces
of work are ejected by pushing in rod A.

In work on Lincoln-type millers or on straddle-mill work,
the return table movement must be long in order to eliminate
the danger of the operator striking the cutters when unclamp-
ing or withdrawing the rear clamp. The necessity of the extra

Machinery

Fig. 26. Fixture Designed for use on Lincoln Milling Machine

long table return is done away with in the straddle-milling fix-
tures illustrated in Fig. 26. The clamps are operated entirely
from the front of the fixture, thus making it unnecessary for
the operator to reach in near the cutters. Clamps A and B
are operated by the handle C through stud D, rod E, and
stud F. The clamps are withdrawn by lever G, which is piv-
oted on stud H and operates clamp A by means of pin /. The
strap K is connected to the other end of lever G and operates
the rear clamp by pin L.

CHAPTER XIV

PROVIDING FOR UPKEEP IN DESIGNING JIGS
AND FIXTURES

The importance of providing for upkeep in the design of the
various types of fixtures used in manufactuiing work cannot
be over-emphasized. In many cases provision for upkeep can
be incorporated in the design without increasing the first cost
of the fixture to any great extent, while in other instances
considerable extra outlay may be necessary. Much depends
upon the accuracy required in the finished product and the
number of pieces which are to be machined. For example, in
gun work, when great quantities of parts are to be produced,
no expense is spared in making the fixtures in as durable a
manner as possible, and in making provision for the replace-
ment of worn locating points, etc. On machine tool work,
however, discretion must be exercised, so that the expense of
fixtures may be consistent with the required rate of production
and accuracy of the work.

Many factors influence design in this regard. The size and
general character of the work determine the type of machine
on which the fixture is to be used, and, therefore, the need for
stability and strength. The number of pieces to be machined
is a factor which must be considered, for it is apparent that a
small number does not require any special care to be taken in
regard to the matter of upkeep. In drill jig work, the locating
points, bushings, and feet may be made so that they can be
readily replaced when abuse or wear of these parts tends to
cause imperfect work. The probable necessity for replacements
is naturally determined by the rate of production that is re-
quired. Jigs and fixtures are often handled roughly and they
should be constructed to withstand such usage. Milling fixtures
are frequently required to stand very heavy cutting so that

306

PROVISION FOR UPKEEP

307

great rigidity is an important feature in their construction. In
the case of horizontal turret lathe fixtures or others which re-
volve about a fixed center, it may frequently be found desira-
ble to make locating rings, points, or surfaces in such a way
that adjustment can conveniently be made about this center.

Machinery

Fig. 1. Drill Jig for a Receiver Forging

Points Pertaining to Upkeep. — A few noteworthy points of
construction are given herewith: i. Location of the work.
This is of primary importance and the various fixed points
provided in the fixture should be made in such a way that they
can either be readily replaced or adjusted, according to cir-

308 JIG DESIGN

cumstances. 2. The number of pieces to be machined should
receive proper consideration in the design, both in regard to
cost of the fixture and in regard to probable necessity of re-
placements. 3. Weight and rigidity of the fixture. This point
is naturally somewhat dependent upon the class of work for
which it is intended, and the convenience of handling. 4. Gibs.
In the case of indexing or sliding fixtures, suitable provision
should be made for adjustment by means of gibs or straps, in
order that natural wear may be taken up. 5. Revolving fix-
tures. Fixtures which revolve about a fixed center, if subjected
to hard usage or if used for a great number of pieces, may be
advantageously provided with means of adjustment about the
center of revolution. This is a refinement that is very infre-
quently used, and it is not necessary in the majority of cases
unless extreme accuracy is required. There are a few points in
construction which are applicable principally to individual
cases. These will be referred to later.

Drill Jig for a Receiver Forging. — The work Ay shown in
Fig. i, has been previously faced, milled and bored, and tapped
at the end K, leaving four holes C, D, E, and F to be drilled
on the jig shown in the illustration. This type of jig is " built
up" entirely from steel parts, a rectangular plate forming the
base of the jig. The work is laid down on the hardened pin B
and the heads of the two jig bushings C and D which are ground
to a uniform surface. The threaded plug at K is provided with
a knurled head L and draws the end of the receiver up against
the steel block N which is screwed and doweled to the jig base.
A thrust washer is provided at M and a slight float is allowed
between the block and the plug. The stud G is screwed into
the plate and the set-screw H running through it forms an
adjustable stop for the side of the receiver, check-nuts being
provided at /. After the work has been drawn up by the
threaded plug at K, the set-screw in the stud P is used to push
the work over against the point H.

The steel clamp O is slid into position and tightened, and
the set-screw R in the swinging clamp Q at the other end of
the work is brought to bear at that point. The clamp Q is

PROVISION FOR UPKEEP

309

pivoted at V, and slotted at the other end where it is locked by
an application of the screw and washer T and ,5, a steel stud
U acting as a support for this end. The four legs of the jig W
are made of hardened steel, screwed into the plate and pro-
truding through the other
side to act as a rest when
placing the work in posi-
tion. It will be noted in
the construction of this jig
that all parts are easily
replaceable or adjustable
for wear, and that al-
though the jig is somewhat
expensive in first cost, the
provision for upkeep is ex-
cellent. It is obvious that
drilling is done against the
clamps, so that these must
necessarily be made some-
what heavier than would
be necessary if they were
simply required for hold-
ing the work.

Drilling and Reaming
Jig. - The casting A,
shown in Fig. 2, is part of
an electrical machine, and
has been previously turned
and faced. It is required
for this operation that the
work be located by the
previously turned and
faced surfaces. The jig body in this instance is made of cast
iron and is of box section, as shown at 5; it is bored out to
receive the two hardened and ground locating rings E and F.
There are three pins C located 120 degrees apart, which act
as stops for the end of the casting, the ends of the pins being

Fig. 2. Jig with Interchangeable Bushings
for Different Tools used in Machining
Cylindrical Part A

310 JIG DESIGN

rounded so that dirt or chips cannot lodge on them and cause
faulty locating. The pin D simply acts as a stop for locating the
internal bosses on the work; and feet are provided at B so that
the jig casting can be set up on this end for loading purposes.
A swinging clamp J is provided at the open end of the jig,
and this clamp is provided with a rocker G which pivots on the
pin H, slot K being cut for its reception.

A swinging clamp-screw is located at L, which works in the
slot on the end of the clamp /, the nut and washer at M being
used to draw it up firmly. An equalizing action is obtained in
this manner on the swivel H, so that pressure is equally dis-
tributed on the end of the casting. As it was necessary during
the machining of this piece to use several sizes of tools and to
work from both sides of the casting, it was found advisable to
use liner bushings P in order to prevent undue wear. These
bushings are hardened and ground, and forced into position;
and the slip bushings Q are slotted to receive the pin R to pre-
vent them from turning. The steel studs N and O on opposite
sides of the jig body are ground to a uniform surface and act
as feet for the jig. In connection with this jig it is well to note
that all parts subject to wear are readily replaceable, thus
making the life of the jig almost indefinite.

Indexing Fixture for a Clutch Gear. — In every kind of
indexing mechanism one of the chief points in design is to pre-
vent variations in the spacing due to wear on the mechanism.
The fixture shown in Fig. 3 is so arranged that wear on the
indexing points is automatically taken up by the construction
of the device, so that the provision made for its upkeep is excel-
lent. In addition to this feature, the design is not very expensive
and it may be made up at much less cost than many other kinds
of indexing devices. The work A is a clutch gear, the clutch
portion B of which is to be machined in this setting. As the
work has been previously machined all over, it is necessary to
work from the finished surfaces.

The body of the fixture G is of cast iron and it is provided
with two machine steel keys at P\ these keys locate the fixture
on the table by means of the T-slots, and the hold-down bolts
Q lock it securely in position. The revolving portion of the fix-

PROVISION FOR UPKEEP

ture F is also of cast iron and has a bearing all around on the
base, while the central stud C is used as a locator for the work
at its upper end, and holds the revolving portion down firmly
by means of the nut and collar at H. The fitting at this point
is such that the fixture may be revolved readily and yet is not
free enough so that there is any lost motion. A liner bushing
of hardened steel is ground to a nice fit on the central stud at E

Machinery

Fig. 3. Indexing Fixture used for Milling Teeth in Clutch Gear

and will wear almost indefinitely, while an indexing ring L is
forced on the revolving portion F of the fixture, and doweled
in its correct position by the pin V and held in place by the four
screws R. The work is held down firmly on the revolving por-
tion by means of the three clamps /, these being slotted at K
to facilitate rapid removal.

A steel index bolt M of rectangular section is carefully fitted
to the slot in the body of the fixture, and beveled at its inner

20 J

3I2

JIG DESIGN

end 5 so that it enters the angular slots S and T of the index
ring. Clearance is allowed between the end of the bolt and the
bottom of these slots so that wear is automatically taken care
of. A stud O is screwed into the under side of the index bolt
and a stiff coiled spring at N keeps the bolt firmly in position.
The pin U is obviously used for drawing the bolt back and
indexing the fixture. Points worthy of note in the construction
of this fixture are the liner bushing at E, the steel locating
ring L, and the automatic method of taking up wear by the
angular lock bolt M .

Fixture with Inserted Jaws. — The work shown at A in
Fig. 4 is a steel casting which has to be finished on the inside.

Fig. 4. Fixture provided with Interchangeable Jaws for Holding
Different Sizes of Work

These castings are made in two sizes, one of which is i inch
larger than the other. It was desired to use the same fixture for
both pieces in order to avoid the expanse of making two fix-
tures. (The larger piece of work is shown in the illustration.)
For this purpose a fixture D was designed to be screwed to the
end of the lathe spindle in the usual manner. There are four
jaws B which rest in slots around the inside of the fixture, these
jaws being drawn back into their seats by the screws C in order
to be ground in place to the correct diameter. Beyond the
ends of the jaws, the pointed hollow set-screws H are so placed
that they will come opposite to the web portion of the casting.

PROVISION FOR UPKEEP

313

By placing them in this manner it is evident that the entire
width of the web will resist the strain of the screws so that they
will not distort the work. Further than this, the screws H
act as drivers, as they sink slightly into the work when set up.
Two holes G are drilled at opposite sides of the fixture, these
holes being utilized to force the work out of the jaws when
removing it from the fixture.

A hardened and ground tool steel bushing E is placed in
the fixture, and acts as a pilot for the cutter-head used in ma-
chining the work; and it will be noted that the surface F of
the fixture is relieved to permit the passage of the tools through
the work. In machining the smaller piece, it is only necessary

Machinery

Fig. 5. Ring Bevel-gear Fixture provided with Adjustable Clamps

to remove the jaws B and hollow set-screws H, and substitute
those suited for the smaller piece. Therefore, one fixture was
found sufficient to handle both pieces and replacements were
made easy by the construction. Adaptations of this type of
fixture may be made for many varieties of work, when several
pieces are to be handled, and it will be found both efficient
and economical in upkeep.

Bevel-gear Fixture with Adjustable Features. — The work A,
shown in Fig. 5, is a ring bevel-gear blank of heavy section,
which has been partly machined. In this instance the fixture
is really composed of two separate pieces, one of which, B, is

314

JIG DESIGN

screwed to the nose of the spindle while the other, C, is adjustable
on the first piece. In the illustration, piece C is shown clamped
firmly against the body B of the fixture by the steel clamping

Machinery

Fig. 6. Fixture for Holding the Partially Finished Casting A

ring D and the screws E, and it will further be noted that there
is a slight clearance between the outside diameter of the body B
and the inside of part C. Three set-screws F are equidistantly

PROVISION FOR UPKEEP 315

placed around the periphery of the ring C and these set-screws
are furnished with check-nuts as shown. By loosening the
collar D and manipulating set-screws F, the working portions of
the fixture can be readily trued up when they become slightly out
of true through use or abuse. A steel locating ring N is forced
on the ring C and is ground to the size of the interior gear.

The method of clamping is somewhat out of the ordinary,
consisting of the use of three clamps G and an operating screw /,
and a floating collar K. The three clamps are placed 1 20
degrees apart and have slightly oversize holes through which
the screws H pass. These screws have a ball surface on the
under side of the collar corresponding to a similar depression
in the clamps themselves. A steel bushing M is fitted to the
body B of the fixture, and is threaded with a coarse pitch thread
which corresponds to that on the operating screw /. After
the clamps G have been swung into place on the ring gear, a
few turns of the screw / sets all three of them with a uniform
pressure through the medium of the spherical collar K which
bears against their inner sides. Although a fixture of this kind
is somewhat expensive in first cost, all the parts can be readily
replaced at a minimum expense and the fixture may also be
kept true with the center of rotation of the spindle with very
little trouble.

Fixture for a Hub Casting. — The work At shown in Fig. 6,
is a hub casting which has been previously machined on the
surfaces B, C, and D. The fixture E on which it is held for
subsequent operations is made of cast iron; it is centered on
the table by the plug F and held down by the screws G which
enter the table T-slots. A steel locating ring H is forced on
the body of the fixture and forms the point of location for the
work. Three studs / are set 120 degrees apart in the base; and
they are surface ground to the correct height to support the
work. This arrangement makes locations positive regardless of
chips or dirt. The clamps K hold the work down on the pins /.
Features of this fixture are the ease of replacement of the locating
rings and points, and freedom from trouble which might be
caused by an accumulation of chips or dirt.

INDEX

PAGE

Abrasive for lapping jig bushings 81

Adjustable bevel-gear fixture 313

Adjustable boring jigs 198

Adjustable fixtures, for bronze worm-gear sector 256

for special bevel-gear blanks 248

for turret lathes and vertical boring mills 242

for vertical boring mill 251

important points in design 242

milling, for angular work 214

turret lathe, for different diameters 246

with means of maintaining accuracy 249

Adjustable locating points 97

Adjustable stops 92

special types 99

Allowance for grinding and lapping bushings, table 79

Angular and lateral adjustment, fixture for 217

Angular and straight drilling, jig for 173

Angular work, adjustable milling fixture for 214

Arbor for jig bushings 85

Attachment for milling on drill jig 177

Automatic locating devices for drill jig 151

Bevel-gear blanks, adjustable fixtures for 248

Bevel-gear fixture with adjustable features 313

Binders or shoes, dimensions, table 99

Bolt, hook, for clamping work 115

Boring and drill jig, combinations 209

Boring bar, supported by jig on one side of hole 200

using work to guide 208

Boring jigs 195

adjustable 198

designs 203

four-part 206

multiple 202

of simple design 196

supported on work 199

Boring mills, vertical, adjustable fixtures for 242, 251

Bosses in pistons, jig for facing 181

Box jigs 15

31?

3l8 INDEX

Box or closed jigs, design of 45

examples of 56

Bushing holders, plate for multiple drilling 88

Bushings, drill, driving fit allowances, table 88

drill, removable type, table 76

drill, stationary type, table of dimensions 71

drill, types of 71

floating, and locating vees applied to drill jig 262

guide, attached to drills 90

guide, special desgin 78

jig 68

jig, allowances for grinding and lapping, table 79

jig, arbor for 85

jig, driving fit allowances 87

jig, for rose chucking reamers, table 77

jig, grinding and lapping 80

jig, hardening 80

jig, materials for 69

jig, method of making 79

jig, screw type 77

jig, stationary, dimensions of 70

jig, used as locating means 94

jig, wheels for internal grinding 83

lining, table of dimensions 72

loose, means for preventing them from turning 73

removable 68

removable, dimensions of 75

screw, general notes 91

screw, used as locating means 94

sliding, used as locating means 94

slip, general note 91

Cam clamping devices 134, 144

Cam-operated clamping slide on drill jig 154

Chucking fixture with floating clamps and taper locating plug 267

Chuck jaws with floating locating points 274

Chuck, piston, with floating clamping features 272

two-jaw, with floating jaw 269

Clamping and locating devices, three-point 277

Clamping by means of screws 1 18 .

Clamping devices 6

application of floating principle 258

cam 134

duplex, on drill jig . . 194

eccentric 133

floating principle 257

for jigs no

special 288

INDEX 319

Clamping members, lever- and spring-operated, on jig 159

Clamping ring, floating, on grinding fixture 275

Clamping slide, cam-operated, on drill jig 154

Clamping, wedges or taper gibs for '..... 130

Clamps, different types applied to jigs 136

floating, and locator, applied to milling fixture 265

floating, and taper locating plug for chucking fixture 267

floating, applied to piston drill jig 260

floating, for piston chuck 272

for jigs 28

for jigs, types of no

multiple, arranged to equalize pressure 293

quick releasing 142

two-point, attached to jig cover 128

which exert combined inward and downward pressure 290

Closed or box jigs, design of 45

examples of 56

Clutches, indexing fixture for milling ( 220

Clutch gear, indexing fixture for 310

Collar-head screws, dimensions, table 116

Combination drill and boring jig 209

Continuous milling fixture 223

Cross-drilling pistons, jigs for 1 79

Cup and cone locating points for jigs 94

Cylinder flange jig .- • • • T3

Cylinder liner, recoil, profile milling fixture for 233

Deep-hole drilling in studs, jig for 171

Defects common to jig design 107

Design of jigs, application of clamps 136

boring 203

closed or box 45

common defects 107

details of 19

general remarks 9

open type 25

summary of principles 10

Dial plates, power press, jig for drilling 193

Drawings for jigs 21

Drill and boring jig, combination 209

Drill bushings, driving fit allowances, table . 88

removable table 76

stationary, table of dimensions 71

types of 71

Drilling and reaming jig 309

Drilling jig, for use in vise 170

Drill jig, designed for rapid indexing 163

equipped with duplex clamping device 194

320 INDEX

equipped with floating bushings and locating vees 262

equipped with milling attachment 177

examples of 151

for fork links 160

for machining half holes 161

for power press dial plates 193

for rough collar 261

multiple, for yoke ends 169

multiple, reversible type 190

open, design of 25

open, examples of 33

open type 13

open type, design of 21

piston, with floating clamps 260

quick-operating 173

with automatic locating devices 151

with cam-operated clamping slide 154

Driving fit allowances, for drill bushings, table 88

for jig bushings 87

Duplex clamping device on drill jig 194

Duplex fixture 213

for routing oil-grooves 234

Eccentric clamping devices 133

Ejecting device on milling fixture 304

Equalizing types of clamping devices 293

Facing bosses in pistons, jig for 181

Feet for jigs 7, 28

table of dimensions 29

Fixture, for Lincoln type milling machine 305

having interchangeable jaws 312

milling 211

planing 234

Flange jig ' 13

Floating bushings and locating vees applied to drill jig 262

Floating clamping features, for piston chuck 272

Floating clamping ring on grinding fixture 275

Floating clamps and locator applied to milling fixture 265

Floating clamps and taper locating plug, for chucking fixture 267

Floating clamps applied to piston drill jig 260

Floating jaw for two-jaw chuck 269

Floating locating points, for chuck jaws 274

Floating pressure compensator, for locating device 267

Floating principle, as applied to fixture work 257

important points in application 258

Flywheel fixture, three-point support 279

Fork links, drill jig for 160

INDEX 321

Gang-planing fixtures 239

Gear blanks, bevel-, adjustable fixtures for 248

Gear, clutch, indexing fixture for 310

Gear fixture, bevel-, with adjustable features 313

Gibs or wedges, for clamping 130

Grinding and lapping bushings 80

allowances for, table 79

Grinding fixture with floating clamping ring 275

Grinding jig bushings, externally 85

wheels for internal 83

Guide bushings attached to drills 90

special designs 78

H^lf holes, jig for drilling 161

Handwheels, jig for drilling rims 42

star, for jigs, table 121

Hardening jig bushings 80

Holes used as means of locating work 105

Hook-bolts, for clamping work 115

Indexing, drill jig designed for rapid 163

Indexing fixture, for clutch gear 310

for milling clutches 220

milling, for roller separator 219

Indexing jigs, mounted on trunnions 167

operated by hand-lever and foot-treadle 156

provided with work-locating devices 164

Interchangeable jaws on fixture : 312

Jaws, chuck, with floating locating points 274

detachable, for vise 212

Jig attachments for drilling in vises 186

Jig bushings 68

arbor for 85

driving fit allowance 87

for rose chucking reamers, table 77

grinding and lapping 80

hardening 80

materials for 69

methods of making 79

screw 77

stationary, dimensions 70

Jig clamping devices 6, 1 10

special 288

Jig design, applications of clamps to 136

boring 203

common defects in 107

details of 19

322

INDEX

general procedure 3

general remarks 9

principles of i

summary of principles 10

Jig drawings 21

Jig feet 7, 28

table of dimensions % 29

Jig locating points 5, 92

adjustable, for work 97

Jigs, adjustable boring ' 198

alignment of, when holes are at an angle 207

boring 195

boring, of simple design 196

boring, supported on work 199

box 15

box or closed, design of 45

clamps for 28

combination boring and drill 209

drill, designed for rapid indexing 163

drill, equipped with floating bushings and locating vees 262

drill, equipped with milling attachment 177

drill, examples of 151

drill, for fork links 160

drill, for machining half holes 161

drill, for rough collar 261

drilling and reaming 309

drill, quick-operating 173

drill, with automatic locating devices 151

drill, with cam-operated clamping slide 154

examples of closed or box 56

for boring holes that are not parallel 201

for cross-drilling pistons 179

for drilling at an angle 55

for drilling deep holes in studs 171

for drilling handwheel rim 42

for drilling power press dial plates 193

for drilling ring 156

for facing bosses in pistons 181

for multiple boring 202

for straight and angular drilling 173

for supporting bar on one side of hole 200

four-part boring 206

having rockers upon which to be turned over 162

indexing, mounted on trunnions 167-

indexing, operated by hand-lever and foot- treadle 156

indexing, provided with work-locating devices 164

locating work by means of pins and studs 92

materials for . . . . 8

INDEX 323

mutiple drill, for yoke ends 169

multiple drilling, reversible type 190

open, design of 25

open drill, examples of 33

open type 13

open type, design of 21

piston drill, with floating clamps 260

screws and nuts for, tables 116

screw tightening devices for 1 18

star handwheels for, table 121

swinging leaves for 1 23

types of ii

universal 183

vise type 170

weight of 7

with lever- and spring-operated clamping members 159

Jigs and fixtures i

difference between 3

object of i

providing for upkeep 306

special mechanisms for 288

Jig-screw latches, dimensions, table 122

Keyways used as means of locating work 106

Knobs, dimensions, table 121

Lap, external, for jig bushings 87

for jig bushings 81

Lapping and grinding bushings 80

allowances for, table 79

Lapping jig bushings, abrasives used 81

Latches for jigs, dimensions, table 122

Latch nuts, dimensions, table 121

Lathe carriage casting, planing fixture for 235

Leaves, swinging, for jigs 123

Liner, recoil cylinder, profile milling fixture for 233

Lining bushings, table of dimensions 72

Locating and clamping devices, three-point 277

Locating, by keyways in the work 106

by means of V-blocks 92

Locating devices, automatic, for drill jig 151

double three-point 285

special, on jig 164

with floating pressure compensator 267

Locating in jigs by means of pins and studs 92

Locating points 92

adjustable 97

cup and cone 94

324

INDEX

floating, for chuck jaws ............................................ 274

for work .......................................................... 5

Locating vees and floating bushings applied to drill jig ................... 262

Locating work, by means of screw and sliding bushings ................... 94

from finished holes .................... ............................. 105

Locator and floating clamps applied to milling fixture .................... 265

Locking trigger for swinging bushing plate .............................. 126

Lubrication of jigs ................................................... 59

Materials, for jig bushings ........................................... 69

for jigs ........................................................... 8

Milling attachment applied to drill jig ................................. 177

Milling fixtures ...................................................... 211

for angular work .................................................. 214

for continuous milling ........................................... ... 223

having lateral and angular adjustment ................................ 217

indexing, for clutches .............................................. 220

indexing, for roller separator ........................................ 219

lever-operated, for milling oil-groove in bushing ....................... 218

profile, for recoil cylinder liner ...................................... 233

radial ............................................................ 224

straddle, for milling to given length ................................. 213

with floating clamps and locator ..................................... 265

Multiple boring, jigs for .............................................. 202

Multiple drilling jig of reversible type .................................. 190

Multiple drilling plate, bushing holders for .............................. 88

Multiple drill jig for yoke ends ........................................ 169

Nuts, latch, dimensions, table ........................................ 121

, duplex fixture for routing ................................. 234

in bushings, lever-operated fixture for milling ....................... 218

Open drill jigs, design of .............................................. 21

examples of ....................................................... 33

Open jigs, design of .................................................. 25

Open type of drill jigs ................................................ 13

Pins and studs used in jigs as locating means ........................... 92

Piston chuck with floating clamping features ............................ 272

Piston drill jig, with floating clamps ................................... 260

Pistons, jigs for cross-drilling .......................................... 1 79

jigs for facing bosses ............................................... 181

Pivoted type of radial fixture ......................................... 227

Planing fixtures ..................................................... 234

for lathe carriage casting ........................................... 235

gang ............................................................ 239

radial ............................................................ 241

Plate bushing holders for multiple drilling .............................. 88

INDEX 325

Pot casting, three-point fixture 280

Profile milling fixture for recoil cylinder liner 233

Quick-operating drill jig 1 73

Quick-release on milling fixture 103

Radial fixtures, for gear cutting operation 229

milling 224

milling, curved slot type 225

milling, pivoted type 227

planing 241

with hand- and power-operated feed 231

Rapid-operating drill jig 1 73

Reaming and drilling jig 309

Removable bushings 68

dimensions of 75

drill, table 76

Reversible multiple drilling jig 190

Ring jig, internal clamping type 156

Rockers on jig to facilitate turning it over 162

Rose chucking reamers, bushing for, table 77

Screw bushings 77

general notes 91

used as Icoating means 94

Screw tightening devices 118

Screws, collar-head, for jigs, table 116

for jig feet, table of dimensions 29

locating for jigs 28

thumb-, dimensions, table 116, 122

Shoes or binders, dimensions, table 99

Sliding points, dimensions of, table 99

Slip bushings, general notes 91

used as locating means 94

Slot, rough-milling, with radial fixture 225

Spring latch for holding jig cover 127

Star handwheels for jigs, table 121

Stationary drill bushings, table of dimensions 71

Stationary jig bushings, dimensions of 70

Stops, adjustable 92

adjustable, special types 99

Straddle-milling fixture, for milling to given length 213

Straps for clamping work in jigs no

Studs and pins used as locating means in jigs 92

Swinging leaves for jigs 123

Taper gibs or wedges, for clamping 130

Three-point fixture for pot casting 280

326 INDEX

Three-point locating and clamping devices 277

Three-point locating device, double .- 285

Three-point principle, application to fixtures 276

Three-point support for flywheel fixture 279

Thumb-nuts, dimensions, table 1 16

Thumb-screws, dimensions, table 116, 122

Trunnion type of indexing jigs 167

Turret lathes, adjustable fixtures for 242

Two-jaw chuck, with floating jaw 269

Types of jigs n

Universal jigs 183

Upkeep, providing for, in jig and fixture design 306

V-blocks used as locating means in jigs 92

Vertical boring mills, adjustable fixtures for 242, 251

Vise drilling jig , 1 70

Vise jaws, detachable 212

Vises provided with drill jig attachments 186

"Wedge or taper gibs for clamping 130

Weight of jigs 7

Wing-nuts, dimensions, table 116

Work-locating device on indexing jig 164

Worm-gear sector, adjustable fixture for 256

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Full text of "Jig and fixture design, a treatise covering the principles of jig and fixture design, the important constructional details, and many different types of work-holding devices used in interchangeable manufacture"

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